no-inner-declarations

Outside strict mode, a function declared inside an if or a loop is also visible after the block, but it only has a value once the block has run. Whether a call works depends on which branch was taken.

In strict mode the function belongs to its block, like a let, so by default it isn't reported there. Modules and class bodies are always strict. That leaves CommonJS files and scripts without "use strict".

Configure#

Off by default. To turn it on:

bunfig.toml

[lint.rules]
"no-inner-declarations" = "error" # or "warn"

Every option, set to its default:

bunfig.toml

[lint.rules]
"no-inner-declarations" = [
  "error",
  "functions", # "functions" or "both"
  {
    blockScopedFunctions = "allow", # "allow" or "disallow"
  },
]

Examples#

logger.cjs1 problem

if (process.env.DEBUG) {
  function log(message) {
    console.log(message);
  }
}

log("ready"); // TypeError unless DEBUG is set

logger.cjsNo problems

function log(message) {
  if (process.env.DEBUG) {
    console.log(message);
  }
}

log("ready");

Not reported either, because the file is in strict mode and log stays in its block:

logger.cjsNo problems

"use strict";

if (process.env.DEBUG) {
  function log(message) {
    console.log(message);
  }
  log("ready");
}

Options#

bunfig.toml

[lint.rules]
no-inner-declarations = ["error", "both", { blockScopedFunctions = "disallow" }]

The first option says what to look at:

Option	What it does
`"functions"` (default)	Report `function` declarations in nested blocks.
`"both"`	Also report `var` declarations in nested blocks.

A var belongs to the whole function, no matter which block it's written in:

example.jswith "both"1 problem

if (user.isAdmin) {
  var role = "admin";
}

example.jswith "both"No problems

let role;
if (user.isAdmin) {
  role = "admin";
}

The second option is an object:

Option	Default	What it does
`blockScopedFunctions`	`"allow"`	With `"disallow"`, report functions in nested blocks in strict mode too.
`namespaces`	`"disallow"`	Only for an oxlint config, where the rule also reports declarations directly inside a TypeScript `namespace`. `"allow"` turns that off. `bunfig.toml` rejects this option.

example.jswith "functions", { "blockScopedFunctions": "disallow" }1 problem

if (process.env.DEBUG) {
  function log(message) {
    console.log(message);
  }
  log("ready");
}