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Bun

Node.js module

repl

Not implemented in Bun

Not implemented. Use Bun's built-in REPL (`bun run` with no arguments or `bun repl`).

  • class Recoverable

    Indicates a recoverable error that a REPLServer can use to support multi-line input.

    • cause?: unknown

      The cause of the error.

    • message: string
    • name: string
    • stack?: string
    • static stackTraceLimit: number

      The maximum number of stack frames to capture.

    • targetObject: object,
      constructorOpt?: Function
      ): void;

      Creates a .stack property on targetObject, which when accessed returns a string representing the location in the code at which Error.captureStackTrace() was called.

      const myObject = {};
Error.captureStackTrace(myObject);
myObject.stack;  // Similar to `new Error().stack`

      The first line of the trace will be prefixed with ${myObject.name}: ${myObject.message}.

      The optional constructorOpt argument accepts a function. If given, all frames above constructorOpt, including constructorOpt, will be omitted from the generated stack trace.

      The constructorOpt argument is useful for hiding implementation details of error generation from the user. For instance:

      function a() {
  b();
}

function b() {
  c();
}

function c() {
  // Create an error without stack trace to avoid calculating the stack trace twice.
  const { stackTraceLimit } = Error;
  Error.stackTraceLimit = 0;
  const error = new Error();
  Error.stackTraceLimit = stackTraceLimit;

  // Capture the stack trace above function b
  Error.captureStackTrace(error, b); // Neither function c, nor b is included in the stack trace
  throw error;
}

a();
    • static isError(
      value: unknown
      ): value is Error;

      Check if a value is an instance of Error

      @param value

      The value to check

      @returns

      True if the value is an instance of Error, false otherwise

    • err: Error,
      stackTraces: CallSite[]
      ): any;

  • class REPLServer

    Instances of repl.REPLServer are created using the start method or directly using the JavaScript new keyword.

    import repl from 'node:repl';

const options = { useColors: true };

const firstInstance = repl.start(options);
const secondInstance = new repl.REPLServer(options);
    • readonly commands: ReadOnlyDict<REPLCommand>

      The commands registered via replServer.defineCommand().

    • readonly completer: Completer | AsyncCompleter

      Specified in the REPL options, this is the function to use for custom Tab auto-completion.

    • readonly context: Context

      The vm.Context provided to the eval function to be used for JavaScript evaluation.

    • readonly cursor: number

      The cursor position relative to rl.line.

      This will track where the current cursor lands in the input string, when reading input from a TTY stream. The position of cursor determines the portion of the input string that will be modified as input is processed, as well as the column where the terminal caret will be rendered.

    • readonly editorMode: boolean

      A value indicating whether the REPL is currently in "editor mode".

    • readonly eval: REPLEval

      Specified in the REPL options, this is the function to be used when evaluating each given line of input. If not specified in the REPL options, this is an async wrapper for the JavaScript eval() function.

    • readonly ignoreUndefined: boolean

      Specified in the REPL options, this is a value indicating whether the default writer function should output the result of a command if it evaluates to undefined.

    • readonly input: ReadableStream

      The Readable stream from which REPL input will be read.

    • readonly last: any

      The last evaluation result from the REPL (assigned to the _ variable inside of the REPL).

    • readonly lastError: any

      The last error raised inside the REPL (assigned to the _error variable inside of the REPL).

    • readonly line: string

      The current input data being processed by node.

      This can be used when collecting input from a TTY stream to retrieve the current value that has been processed thus far, prior to the line event being emitted. Once the line event has been emitted, this property will be an empty string.

      Be aware that modifying the value during the instance runtime may have unintended consequences if rl.cursor is not also controlled.

      If not using a TTY stream for input, use the 'line' event.

      One possible use case would be as follows:

      const values = ['lorem ipsum', 'dolor sit amet'];
const rl = readline.createInterface(process.stdin);
const showResults = debounce(() => {
  console.log(
    '\n',
    values.filter((val) => val.startsWith(rl.line)).join(' '),
  );
}, 300);
process.stdin.on('keypress', (c, k) => {
  showResults();
});
    • readonly output: WritableStream

      The Writable stream to which REPL output will be written.

    • readonly replMode: typeof REPL_MODE_SLOPPY | typeof REPL_MODE_STRICT

      Specified in the REPL options, this is a flag that specifies whether the default eval function should execute all JavaScript commands in strict mode or default (sloppy) mode. Possible values are:

      • repl.REPL_MODE_SLOPPY - evaluates expressions in sloppy mode.
      • repl.REPL_MODE_STRICT - evaluates expressions in strict mode. This is equivalent to prefacing every repl statement with 'use strict'.
    • readonly terminal: boolean
    • readonly underscoreAssigned: boolean

      A value indicating whether the _ variable has been assigned.

    • readonly underscoreErrAssigned: boolean

      A value indicating whether the _error variable has been assigned.

    • readonly useColors: boolean

      Specified in the REPL options, this is a value indicating whether the default writer function should include ANSI color styling to REPL output.

    • readonly useGlobal: boolean

      Specified in the REPL options, this is a value indicating whether the default eval function will use the JavaScript global as the context as opposed to creating a new separate context for the REPL instance.

    • readonly writer: REPLWriter

      Specified in the REPL options, this is the function to invoke to format the output of each command before writing to outputStream. If not specified in the REPL options, this will be a wrapper for util.inspect.

    • static captureRejections: boolean

      Value: boolean

      Change the default captureRejections option on all new EventEmitter objects.

    • readonly static captureRejectionSymbol: typeof captureRejectionSymbol

      Value: Symbol.for('nodejs.rejection')

      See how to write a custom rejection handler.

    • static defaultMaxListeners: number

      By default, a maximum of 10 listeners can be registered for any single event. This limit can be changed for individual EventEmitter instances using the emitter.setMaxListeners(n) method. To change the default for allEventEmitter instances, the events.defaultMaxListeners property can be used. If this value is not a positive number, a RangeError is thrown.

      Take caution when setting the events.defaultMaxListeners because the change affects all EventEmitter instances, including those created before the change is made. However, calling emitter.setMaxListeners(n) still has precedence over events.defaultMaxListeners.

      This is not a hard limit. The EventEmitter instance will allow more listeners to be added but will output a trace warning to stderr indicating that a "possible EventEmitter memory leak" has been detected. For any single EventEmitter, the emitter.getMaxListeners() and emitter.setMaxListeners() methods can be used to temporarily avoid this warning:

      import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once('event', () => {
  // do stuff
  emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});

      The --trace-warnings command-line flag can be used to display the stack trace for such warnings.

      The emitted warning can be inspected with process.on('warning') and will have the additional emitter, type, and count properties, referring to the event emitter instance, the event's name and the number of attached listeners, respectively. Its name property is set to 'MaxListenersExceededWarning'.

    • readonly static errorMonitor: typeof errorMonitor

      This symbol shall be used to install a listener for only monitoring 'error' events. Listeners installed using this symbol are called before the regular 'error' listeners are called.

      Installing a listener using this symbol does not change the behavior once an 'error' event is emitted. Therefore, the process will still crash if no regular 'error' listener is installed.

    • [Symbol.asyncIterator](): AsyncIterator<string>;
    • error: Error,
      event: string | symbol,
      ...args: AnyRest
      ): void;

    • Alias for rl.close().

    • event: string,
      listener: (...args: any[]) => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset
      event: 'close',
      listener: () => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset
      event: 'line',
      listener: (input: string) => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset
      event: 'pause',
      listener: () => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset
      event: 'resume',
      listener: () => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset
      event: 'SIGCONT',
      listener: () => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset
      event: 'SIGINT',
      listener: () => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset
      event: 'SIGTSTP',
      listener: () => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset
      event: 'exit',
      listener: () => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset
      event: 'reset',
      listener: (context: Context) => void
      ): this;

      events.EventEmitter

      1. close - inherited from readline.Interface
      2. line - inherited from readline.Interface
      3. pause - inherited from readline.Interface
      4. resume - inherited from readline.Interface
      5. SIGCONT - inherited from readline.Interface
      6. SIGINT - inherited from readline.Interface
      7. SIGTSTP - inherited from readline.Interface
      8. exit
      9. reset

    • The replServer.clearBufferedCommand() method clears any command that has been buffered but not yet executed. This method is primarily intended to be called from within the action function for commands registered using the replServer.defineCommand() method.

    • close(): void;

      The rl.close() method closes the Interface instance and relinquishes control over the input and output streams. When called, the 'close' event will be emitted.

      Calling rl.close() does not immediately stop other events (including 'line') from being emitted by the Interface instance.

    • keyword: string,
      cmd: REPLCommandAction | REPLCommand
      ): void;

      The replServer.defineCommand() method is used to add new .-prefixed commands to the REPL instance. Such commands are invoked by typing a . followed by the keyword. The cmd is either a Function or an Object with the following properties:

      The following example shows two new commands added to the REPL instance:

      import repl from 'node:repl';

const replServer = repl.start({ prompt: '> ' });
replServer.defineCommand('sayhello', {
  help: 'Say hello',
  action(name) {
    this.clearBufferedCommand();
    console.log(`Hello, ${name}!`);
    this.displayPrompt();
  },
});
replServer.defineCommand('saybye', function saybye() {
  console.log('Goodbye!');
  this.close();
});

      The new commands can then be used from within the REPL instance:

      > .sayhello Node.js User
Hello, Node.js User!
> .saybye
Goodbye!
      @param keyword

      The command keyword (without a leading . character).

      @param cmd

      The function to invoke when the command is processed.

    • preserveCursor?: boolean
      ): void;

      The replServer.displayPrompt() method readies the REPL instance for input from the user, printing the configured prompt to a new line in the output and resuming the input to accept new input.

      When multi-line input is being entered, an ellipsis is printed rather than the 'prompt'.

      When preserveCursor is true, the cursor placement will not be reset to 0.

      The replServer.displayPrompt method is primarily intended to be called from within the action function for commands registered using the replServer.defineCommand() method.

    • event: string | symbol,
      ...args: any[]
      ): boolean;

      Synchronously calls each of the listeners registered for the event named eventName, in the order they were registered, passing the supplied arguments to each.

      Returns true if the event had listeners, false otherwise.

      import { EventEmitter } from 'node:events';
const myEmitter = new EventEmitter();

// First listener
myEmitter.on('event', function firstListener() {
  console.log('Helloooo! first listener');
});
// Second listener
myEmitter.on('event', function secondListener(arg1, arg2) {
  console.log(`event with parameters ${arg1}, ${arg2} in second listener`);
});
// Third listener
myEmitter.on('event', function thirdListener(...args) {
  const parameters = args.join(', ');
  console.log(`event with parameters ${parameters} in third listener`);
});

console.log(myEmitter.listeners('event'));

myEmitter.emit('event', 1, 2, 3, 4, 5);

// Prints:
// [
//   [Function: firstListener],
//   [Function: secondListener],
//   [Function: thirdListener]
// ]
// Helloooo! first listener
// event with parameters 1, 2 in second listener
// event with parameters 1, 2, 3, 4, 5 in third listener
      event: 'close'
      ): boolean;
      event: 'line',
      input: string
      ): boolean;
      event: 'pause'
      ): boolean;
      event: 'resume'
      ): boolean;
      event: 'SIGCONT'
      ): boolean;
      event: 'SIGINT'
      ): boolean;
      event: 'SIGTSTP'
      ): boolean;
      event: 'exit'
      ): boolean;
      event: 'reset',
      context: Context
      ): boolean;
    • eventNames(): string | symbol[];

      Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or Symbols.

      import { EventEmitter } from 'node:events';

const myEE = new EventEmitter();
myEE.on('foo', () => {});
myEE.on('bar', () => {});

const sym = Symbol('symbol');
myEE.on(sym, () => {});

console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]

    • Returns the real position of the cursor in relation to the input prompt + string. Long input (wrapping) strings, as well as multiple line prompts are included in the calculations.

    • getMaxListeners(): number;

      Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to EventEmitter.defaultMaxListeners.

    • getPrompt(): string;

      The rl.getPrompt() method returns the current prompt used by rl.prompt().

      @returns

      the current prompt string

    • eventName: string | symbol,
      listener?: Function
      ): number;

      Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.

      @param eventName

      The name of the event being listened for

      @param listener

      The event handler function

    • eventName: string | symbol
      ): Function[];

      Returns a copy of the array of listeners for the event named eventName.

      server.on('connection', (stream) => {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection')));
// Prints: [ [Function] ]
    • off<K>(
      eventName: string | symbol,
      listener: (...args: any[]) => void
      ): this;

      Alias for emitter.removeListener().

    • event: string,
      listener: (...args: any[]) => void
      ): this;

      Adds the listener function to the end of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.

      server.on('connection', (stream) => {
  console.log('someone connected!');
});

      Returns a reference to the EventEmitter, so that calls can be chained.

      By default, event listeners are invoked in the order they are added. The emitter.prependListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.

      import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.on('foo', () => console.log('a'));
myEE.prependListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
//   b
//   a
      @param listener

      The callback function

      event: 'close',
      listener: () => void
      ): this;
      event: 'line',
      listener: (input: string) => void
      ): this;
      event: 'pause',
      listener: () => void
      ): this;
      event: 'resume',
      listener: () => void
      ): this;
      event: 'SIGCONT',
      listener: () => void
      ): this;
      event: 'SIGINT',
      listener: () => void
      ): this;
      event: 'SIGTSTP',
      listener: () => void
      ): this;
      event: 'exit',
      listener: () => void
      ): this;
      event: 'reset',
      listener: (context: Context) => void
      ): this;
    • event: string,
      listener: (...args: any[]) => void
      ): this;

      Adds a one-time listener function for the event named eventName. The next time eventName is triggered, this listener is removed and then invoked.

      server.once('connection', (stream) => {
  console.log('Ah, we have our first user!');
});

      Returns a reference to the EventEmitter, so that calls can be chained.

      By default, event listeners are invoked in the order they are added. The emitter.prependOnceListener() method can be used as an alternative to add the event listener to the beginning of the listeners array.

      import { EventEmitter } from 'node:events';
const myEE = new EventEmitter();
myEE.once('foo', () => console.log('a'));
myEE.prependOnceListener('foo', () => console.log('b'));
myEE.emit('foo');
// Prints:
//   b
//   a
      @param listener

      The callback function

      event: 'close',
      listener: () => void
      ): this;
      event: 'line',
      listener: (input: string) => void
      ): this;
      event: 'pause',
      listener: () => void
      ): this;
      event: 'resume',
      listener: () => void
      ): this;
      event: 'SIGCONT',
      listener: () => void
      ): this;
      event: 'SIGINT',
      listener: () => void
      ): this;
      event: 'SIGTSTP',
      listener: () => void
      ): this;
      event: 'exit',
      listener: () => void
      ): this;
      event: 'reset',
      listener: (context: Context) => void
      ): this;
    • pause(): this;

      The rl.pause() method pauses the input stream, allowing it to be resumed later if necessary.

      Calling rl.pause() does not immediately pause other events (including 'line') from being emitted by the Interface instance.

    • event: string,
      listener: (...args: any[]) => void
      ): this;

      Adds the listener function to the beginning of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventName and listener will result in the listener being added, and called, multiple times.

      server.prependListener('connection', (stream) => {
  console.log('someone connected!');
});

      Returns a reference to the EventEmitter, so that calls can be chained.

      @param listener

      The callback function

      event: 'close',
      listener: () => void
      ): this;
      event: 'line',
      listener: (input: string) => void
      ): this;
      event: 'pause',
      listener: () => void
      ): this;
      event: 'resume',
      listener: () => void
      ): this;
      event: 'SIGCONT',
      listener: () => void
      ): this;
      event: 'SIGINT',
      listener: () => void
      ): this;
      event: 'SIGTSTP',
      listener: () => void
      ): this;
      event: 'exit',
      listener: () => void
      ): this;
      event: 'reset',
      listener: (context: Context) => void
      ): this;
    • event: string,
      listener: (...args: any[]) => void
      ): this;

      Adds a one-timelistener function for the event named eventName to the beginning of the listeners array. The next time eventName is triggered, this listener is removed, and then invoked.

      server.prependOnceListener('connection', (stream) => {
  console.log('Ah, we have our first user!');
});

      Returns a reference to the EventEmitter, so that calls can be chained.

      @param listener

      The callback function

      event: 'close',
      listener: () => void
      ): this;
      event: 'line',
      listener: (input: string) => void
      ): this;
      event: 'pause',
      listener: () => void
      ): this;
      event: 'resume',
      listener: () => void
      ): this;
      event: 'SIGCONT',
      listener: () => void
      ): this;
      event: 'SIGINT',
      listener: () => void
      ): this;
      event: 'SIGTSTP',
      listener: () => void
      ): this;
      event: 'exit',
      listener: () => void
      ): this;
      event: 'reset',
      listener: (context: Context) => void
      ): this;
    • preserveCursor?: boolean
      ): void;

      The rl.prompt() method writes the Interface instances configuredprompt to a new line in output in order to provide a user with a new location at which to provide input.

      When called, rl.prompt() will resume the input stream if it has been paused.

      If the Interface was created with output set to null or undefined the prompt is not written.

      @param preserveCursor

      If true, prevents the cursor placement from being reset to 0.

    • query: string,
      callback: (answer: string) => void
      ): void;

      The rl.question() method displays the query by writing it to the output, waits for user input to be provided on input, then invokes the callback function passing the provided input as the first argument.

      When called, rl.question() will resume the input stream if it has been paused.

      If the Interface was created with output set to null or undefined the query is not written.

      The callback function passed to rl.question() does not follow the typical pattern of accepting an Error object or null as the first argument. The callback is called with the provided answer as the only argument.

      An error will be thrown if calling rl.question() after rl.close().

      Example usage:

      rl.question('What is your favorite food? ', (answer) => {
  console.log(`Oh, so your favorite food is ${answer}`);
});

      Using an AbortController to cancel a question.

      const ac = new AbortController();
const signal = ac.signal;

rl.question('What is your favorite food? ', { signal }, (answer) => {
  console.log(`Oh, so your favorite food is ${answer}`);
});

signal.addEventListener('abort', () => {
  console.log('The food question timed out');
}, { once: true });

setTimeout(() => ac.abort(), 10000);
      @param query

      A statement or query to write to output, prepended to the prompt.

      @param callback

      A callback function that is invoked with the user's input in response to the query.

      query: string,
      options: Abortable,
      callback: (answer: string) => void
      ): void;

      The rl.question() method displays the query by writing it to the output, waits for user input to be provided on input, then invokes the callback function passing the provided input as the first argument.

      When called, rl.question() will resume the input stream if it has been paused.

      If the Interface was created with output set to null or undefined the query is not written.

      The callback function passed to rl.question() does not follow the typical pattern of accepting an Error object or null as the first argument. The callback is called with the provided answer as the only argument.

      An error will be thrown if calling rl.question() after rl.close().

      Example usage:

      rl.question('What is your favorite food? ', (answer) => {
  console.log(`Oh, so your favorite food is ${answer}`);
});

      Using an AbortController to cancel a question.

      const ac = new AbortController();
const signal = ac.signal;

rl.question('What is your favorite food? ', { signal }, (answer) => {
  console.log(`Oh, so your favorite food is ${answer}`);
});

signal.addEventListener('abort', () => {
  console.log('The food question timed out');
}, { once: true });

setTimeout(() => ac.abort(), 10000);
      @param query

      A statement or query to write to output, prepended to the prompt.

      @param callback

      A callback function that is invoked with the user's input in response to the query.

    • eventName: string | symbol
      ): Function[];

      Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

      import { EventEmitter } from 'node:events';
const emitter = new EventEmitter();
emitter.once('log', () => console.log('log once'));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners('log');
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on('log', () => console.log('log persistently'));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners('log');

// Logs "log persistently" twice
newListeners[0]();
emitter.emit('log');
    • eventName?: string | symbol
      ): this;

      Removes all listeners, or those of the specified eventName.

      It is bad practice to remove listeners added elsewhere in the code, particularly when the EventEmitter instance was created by some other component or module (e.g. sockets or file streams).

      Returns a reference to the EventEmitter, so that calls can be chained.

    • eventName: string | symbol,
      listener: (...args: any[]) => void
      ): this;

      Removes the specified listener from the listener array for the event named eventName.

      const callback = (stream) => {
  console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);

      removeListener() will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified eventName, then removeListener() must be called multiple times to remove each instance.

      Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that any removeListener() or removeAllListeners() calls after emitting and before the last listener finishes execution will not remove them fromemit() in progress. Subsequent events behave as expected.

      import { EventEmitter } from 'node:events';
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();

const callbackA = () => {
  console.log('A');
  myEmitter.removeListener('event', callbackB);
};

const callbackB = () => {
  console.log('B');
};

myEmitter.on('event', callbackA);

myEmitter.on('event', callbackB);

// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit('event');
// Prints:
//   A
//   B

// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit('event');
// Prints:
//   A

      Because listeners are managed using an internal array, calling this will change the position indices of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the emitter.listeners() method will need to be recreated.

      When a single function has been added as a handler multiple times for a single event (as in the example below), removeListener() will remove the most recently added instance. In the example the once('ping') listener is removed:

      import { EventEmitter } from 'node:events';
const ee = new EventEmitter();

function pong() {
  console.log('pong');
}

ee.on('ping', pong);
ee.once('ping', pong);
ee.removeListener('ping', pong);

ee.emit('ping');
ee.emit('ping');

      Returns a reference to the EventEmitter, so that calls can be chained.

    • resume(): this;

      The rl.resume() method resumes the input stream if it has been paused.

    • n: number
      ): this;

      By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default that helps finding memory leaks. The emitter.setMaxListeners() method allows the limit to be modified for this specific EventEmitter instance. The value can be set to Infinity (or 0) to indicate an unlimited number of listeners.

      Returns a reference to the EventEmitter, so that calls can be chained.

    • prompt: string
      ): void;

      The rl.setPrompt() method sets the prompt that will be written to output whenever rl.prompt() is called.

    • path: string,
      callback: (err: null | Error, repl: this) => void
      ): void;

      Initializes a history log file for the REPL instance. When executing the Node.js binary and using the command-line REPL, a history file is initialized by default. However, this is not the case when creating a REPL programmatically. Use this method to initialize a history log file when working with REPL instances programmatically.

      @param callback

      called when history writes are ready or upon error

    • data: string | Buffer<ArrayBufferLike>,
      key?: Key
      ): void;

      The rl.write() method will write either data or a key sequence identified by key to the output. The key argument is supported only if output is a TTY text terminal. See TTY keybindings for a list of key combinations.

      If key is specified, data is ignored.

      When called, rl.write() will resume the input stream if it has been paused.

      If the Interface was created with output set to null or undefined the data and key are not written.

      rl.write('Delete this!');
// Simulate Ctrl+U to delete the line written previously
rl.write(null, { ctrl: true, name: 'u' });

      The rl.write() method will write the data to the readline Interface's input as if it were provided by the user.

      data: undefined | null | string | Buffer<ArrayBufferLike>,
      key: Key
      ): void;

      The rl.write() method will write either data or a key sequence identified by key to the output. The key argument is supported only if output is a TTY text terminal. See TTY keybindings for a list of key combinations.

      If key is specified, data is ignored.

      When called, rl.write() will resume the input stream if it has been paused.

      If the Interface was created with output set to null or undefined the data and key are not written.

      rl.write('Delete this!');
// Simulate Ctrl+U to delete the line written previously
rl.write(null, { ctrl: true, name: 'u' });

      The rl.write() method will write the data to the readline Interface's input as if it were provided by the user.

    • signal: AbortSignal,
      resource: (event: Event) => void
      ): Disposable;

      Listens once to the abort event on the provided signal.

      Listening to the abort event on abort signals is unsafe and may lead to resource leaks since another third party with the signal can call e.stopImmediatePropagation(). Unfortunately Node.js cannot change this since it would violate the web standard. Additionally, the original API makes it easy to forget to remove listeners.

      This API allows safely using AbortSignals in Node.js APIs by solving these two issues by listening to the event such that stopImmediatePropagation does not prevent the listener from running.

      Returns a disposable so that it may be unsubscribed from more easily.

      import { addAbortListener } from 'node:events';

function example(signal) {
  let disposable;
  try {
    signal.addEventListener('abort', (e) => e.stopImmediatePropagation());
    disposable = addAbortListener(signal, (e) => {
      // Do something when signal is aborted.
    });
  } finally {
    disposable?.[Symbol.dispose]();
  }
}
      @returns

      Disposable that removes the abort listener.

    • emitter: EventEmitter<DefaultEventMap> | EventTarget,
      name: string | symbol
      ): Function[];

      Returns a copy of the array of listeners for the event named eventName.

      For EventEmitters this behaves exactly the same as calling .listeners on the emitter.

      For EventTargets this is the only way to get the event listeners for the event target. This is useful for debugging and diagnostic purposes.

      import { getEventListeners, EventEmitter } from 'node:events';

{
  const ee = new EventEmitter();
  const listener = () => console.log('Events are fun');
  ee.on('foo', listener);
  console.log(getEventListeners(ee, 'foo')); // [ [Function: listener] ]
}
{
  const et = new EventTarget();
  const listener = () => console.log('Events are fun');
  et.addEventListener('foo', listener);
  console.log(getEventListeners(et, 'foo')); // [ [Function: listener] ]
}
    • emitter: EventEmitter<DefaultEventMap> | EventTarget
      ): number;

      Returns the currently set max amount of listeners.

      For EventEmitters this behaves exactly the same as calling .getMaxListeners on the emitter.

      For EventTargets this is the only way to get the max event listeners for the event target. If the number of event handlers on a single EventTarget exceeds the max set, the EventTarget will print a warning.

      import { getMaxListeners, setMaxListeners, EventEmitter } from 'node:events';

{
  const ee = new EventEmitter();
  console.log(getMaxListeners(ee)); // 10
  setMaxListeners(11, ee);
  console.log(getMaxListeners(ee)); // 11
}
{
  const et = new EventTarget();
  console.log(getMaxListeners(et)); // 10
  setMaxListeners(11, et);
  console.log(getMaxListeners(et)); // 11
}
    • static on(
      emitter: EventEmitter,
      eventName: string | symbol,
      options?: StaticEventEmitterIteratorOptions
      ): AsyncIterator<any[]>;
      import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

// Emit later on
process.nextTick(() => {
  ee.emit('foo', 'bar');
  ee.emit('foo', 42);
});

for await (const event of on(ee, 'foo')) {
  // The execution of this inner block is synchronous and it
  // processes one event at a time (even with await). Do not use
  // if concurrent execution is required.
  console.log(event); // prints ['bar'] [42]
}
// Unreachable here

      Returns an AsyncIterator that iterates eventName events. It will throw if the EventEmitter emits 'error'. It removes all listeners when exiting the loop. The value returned by each iteration is an array composed of the emitted event arguments.

      An AbortSignal can be used to cancel waiting on events:

      import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ac = new AbortController();

(async () => {
  const ee = new EventEmitter();

  // Emit later on
  process.nextTick(() => {
    ee.emit('foo', 'bar');
    ee.emit('foo', 42);
  });

  for await (const event of on(ee, 'foo', { signal: ac.signal })) {
    // The execution of this inner block is synchronous and it
    // processes one event at a time (even with await). Do not use
    // if concurrent execution is required.
    console.log(event); // prints ['bar'] [42]
  }
  // Unreachable here
})();

process.nextTick(() => ac.abort());

      Use the close option to specify an array of event names that will end the iteration:

      import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

// Emit later on
process.nextTick(() => {
  ee.emit('foo', 'bar');
  ee.emit('foo', 42);
  ee.emit('close');
});

for await (const event of on(ee, 'foo', { close: ['close'] })) {
  console.log(event); // prints ['bar'] [42]
}
// the loop will exit after 'close' is emitted
console.log('done'); // prints 'done'
      @returns

      An AsyncIterator that iterates eventName events emitted by the emitter

      static on(
      emitter: EventTarget,
      eventName: string,
      options?: StaticEventEmitterIteratorOptions
      ): AsyncIterator<any[]>;
      import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

// Emit later on
process.nextTick(() => {
  ee.emit('foo', 'bar');
  ee.emit('foo', 42);
});

for await (const event of on(ee, 'foo')) {
  // The execution of this inner block is synchronous and it
  // processes one event at a time (even with await). Do not use
  // if concurrent execution is required.
  console.log(event); // prints ['bar'] [42]
}
// Unreachable here

      Returns an AsyncIterator that iterates eventName events. It will throw if the EventEmitter emits 'error'. It removes all listeners when exiting the loop. The value returned by each iteration is an array composed of the emitted event arguments.

      An AbortSignal can be used to cancel waiting on events:

      import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ac = new AbortController();

(async () => {
  const ee = new EventEmitter();

  // Emit later on
  process.nextTick(() => {
    ee.emit('foo', 'bar');
    ee.emit('foo', 42);
  });

  for await (const event of on(ee, 'foo', { signal: ac.signal })) {
    // The execution of this inner block is synchronous and it
    // processes one event at a time (even with await). Do not use
    // if concurrent execution is required.
    console.log(event); // prints ['bar'] [42]
  }
  // Unreachable here
})();

process.nextTick(() => ac.abort());

      Use the close option to specify an array of event names that will end the iteration:

      import { on, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

// Emit later on
process.nextTick(() => {
  ee.emit('foo', 'bar');
  ee.emit('foo', 42);
  ee.emit('close');
});

for await (const event of on(ee, 'foo', { close: ['close'] })) {
  console.log(event); // prints ['bar'] [42]
}
// the loop will exit after 'close' is emitted
console.log('done'); // prints 'done'
      @returns

      An AsyncIterator that iterates eventName events emitted by the emitter

    • static once(
      emitter: EventEmitter,
      eventName: string | symbol,
      options?: StaticEventEmitterOptions
      ): Promise<any[]>;

      Creates a Promise that is fulfilled when the EventEmitter emits the given event or that is rejected if the EventEmitter emits 'error' while waiting. The Promise will resolve with an array of all the arguments emitted to the given event.

      This method is intentionally generic and works with the web platform EventTarget interface, which has no special'error' event semantics and does not listen to the 'error' event.

      import { once, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

process.nextTick(() => {
  ee.emit('myevent', 42);
});

const [value] = await once(ee, 'myevent');
console.log(value);

const err = new Error('kaboom');
process.nextTick(() => {
  ee.emit('error', err);
});

try {
  await once(ee, 'myevent');
} catch (err) {
  console.error('error happened', err);
}

      The special handling of the 'error' event is only used when events.once() is used to wait for another event. If events.once() is used to wait for the 'error' event itself, then it is treated as any other kind of event without special handling:

      import { EventEmitter, once } from 'node:events';

const ee = new EventEmitter();

once(ee, 'error')
  .then(([err]) => console.log('ok', err.message))
  .catch((err) => console.error('error', err.message));

ee.emit('error', new Error('boom'));

// Prints: ok boom

      An AbortSignal can be used to cancel waiting for the event:

      import { EventEmitter, once } from 'node:events';

const ee = new EventEmitter();
const ac = new AbortController();

async function foo(emitter, event, signal) {
  try {
    await once(emitter, event, { signal });
    console.log('event emitted!');
  } catch (error) {
    if (error.name === 'AbortError') {
      console.error('Waiting for the event was canceled!');
    } else {
      console.error('There was an error', error.message);
    }
  }
}

foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
      static once(
      emitter: EventTarget,
      eventName: string,
      options?: StaticEventEmitterOptions
      ): Promise<any[]>;

      Creates a Promise that is fulfilled when the EventEmitter emits the given event or that is rejected if the EventEmitter emits 'error' while waiting. The Promise will resolve with an array of all the arguments emitted to the given event.

      This method is intentionally generic and works with the web platform EventTarget interface, which has no special'error' event semantics and does not listen to the 'error' event.

      import { once, EventEmitter } from 'node:events';
import process from 'node:process';

const ee = new EventEmitter();

process.nextTick(() => {
  ee.emit('myevent', 42);
});

const [value] = await once(ee, 'myevent');
console.log(value);

const err = new Error('kaboom');
process.nextTick(() => {
  ee.emit('error', err);
});

try {
  await once(ee, 'myevent');
} catch (err) {
  console.error('error happened', err);
}

      The special handling of the 'error' event is only used when events.once() is used to wait for another event. If events.once() is used to wait for the 'error' event itself, then it is treated as any other kind of event without special handling:

      import { EventEmitter, once } from 'node:events';

const ee = new EventEmitter();

once(ee, 'error')
  .then(([err]) => console.log('ok', err.message))
  .catch((err) => console.error('error', err.message));

ee.emit('error', new Error('boom'));

// Prints: ok boom

      An AbortSignal can be used to cancel waiting for the event:

      import { EventEmitter, once } from 'node:events';

const ee = new EventEmitter();
const ac = new AbortController();

async function foo(emitter, event, signal) {
  try {
    await once(emitter, event, { signal });
    console.log('event emitted!');
  } catch (error) {
    if (error.name === 'AbortError') {
      console.error('Waiting for the event was canceled!');
    } else {
      console.error('There was an error', error.message);
    }
  }
}

foo(ee, 'foo', ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit('foo'); // Prints: Waiting for the event was canceled!
    • n?: number,
      ...eventTargets: EventEmitter<DefaultEventMap> | EventTarget[]
      ): void;
      import { setMaxListeners, EventEmitter } from 'node:events';

const target = new EventTarget();
const emitter = new EventEmitter();

setMaxListeners(5, target, emitter);
      @param n

      A non-negative number. The maximum number of listeners per EventTarget event.

      @param eventTargets

      Zero or more {EventTarget} or {EventEmitter} instances. If none are specified, n is set as the default max for all newly created {EventTarget} and {EventEmitter} objects.

  • const REPL_MODE_SLOPPY: unique symbol

    A flag passed in the REPL options. Evaluates expressions in sloppy mode.

  • const REPL_MODE_STRICT: unique symbol

    A flag passed in the REPL options. Evaluates expressions in strict mode. This is equivalent to prefacing every repl statement with 'use strict'.

  • const writer: REPLWriter & { options: InspectOptions }

    This is the default "writer" value, if none is passed in the REPL options, and it can be overridden by custom print functions.

  • function start(
    options?: string | ReplOptions

    The repl.start() method creates and starts a REPLServer instance.

    If options is a string, then it specifies the input prompt:

    import repl from 'node:repl';

// a Unix style prompt
repl.start('$ ');

Type definitions

  • interface REPLCommand

    • action: REPLCommandAction

      The function to execute, optionally accepting a single string argument.

    • help?: string

      Help text to be displayed when .help is entered.

  • interface ReplOptions

    • breakEvalOnSigint?: boolean

      Stop evaluating the current piece of code when SIGINT is received, i.e. Ctrl+C is pressed. This cannot be used together with a custom eval function.

    • completer?: Completer | AsyncCompleter

      An optional function used for custom Tab auto completion.

    • eval?: REPLEval

      The function to be used when evaluating each given line of input. Default: an async wrapper for the JavaScript eval() function. An eval function can error with repl.Recoverable to indicate the input was incomplete and prompt for additional lines.

    • ignoreUndefined?: boolean

      If true, specifies that the default writer will not output the return value of a command if it evaluates to undefined.

    • input?: ReadableStream

      The Readable stream from which REPL input will be read.

    • output?: WritableStream

      The Writable stream to which REPL output will be written.

    • preview?: boolean

      Defines if the repl prints output previews or not.

    • prompt?: string

      The input prompt to display.

    • replMode?: typeof REPL_MODE_SLOPPY | typeof REPL_MODE_STRICT

      A flag that specifies whether the default evaluator executes all JavaScript commands in strict mode or default (sloppy) mode. Accepted values are:

      • repl.REPL_MODE_SLOPPY - evaluates expressions in sloppy mode.
      • repl.REPL_MODE_STRICT - evaluates expressions in strict mode. This is equivalent to prefacing every repl statement with 'use strict'.
    • terminal?: boolean

      If true, specifies that the output should be treated as a TTY terminal, and have ANSI/VT100 escape codes written to it. Default: checking the value of the isTTY property on the output stream upon instantiation.

    • useColors?: boolean

      If true, specifies that the default writer function should include ANSI color styling to REPL output. If a custom writer function is provided then this has no effect.

    • useGlobal?: boolean

      If true, specifies that the default evaluation function will use the JavaScript global as the context as opposed to creating a new separate context for the REPL instance. The node CLI REPL sets this value to true.

    • writer?: REPLWriter

      The function to invoke to format the output of each command before writing to output.

  • type REPLCommandAction = (this: REPLServer, text: string) => void
  • type REPLEval = (this: REPLServer, evalCmd: string, context: Context, file: string, cb: (err: Error | null, result: any) => void) => void
  • type REPLWriter = (this: REPLServer, obj: any) => string