bun/no-array-just-to-count

text.split("\n").length copies every line of text into a new array, reads the length, and throws the array away. For a large string, that's a lot of memory for one number. A loop that counts the separator allocates nothing.

Only a literal one-character separator is reported, not a variable or a regular expression.

Configure#

Off by default. To turn it on:

bunfig.toml

[lint.rules]
"bun/no-array-just-to-count" = "error" # or "warn"

Every option, set to its default. The ones that are commented out are unset by default.

bunfig.toml

[lint.rules]
"bun/no-array-just-to-count" = ["error", {
  # countFunction = <string>,
}]

Examples#

example.js1 problem

const lineCount = source.split("\n").length;

example.jsNo problems

function count(text, separator) {
  let found = 0;
  for (let at = text.indexOf(separator); at !== -1; at = text.indexOf(separator, at + 1)) {
    found++;
  }
  return found;
}

const lineCount = count(source, "\n") + 1;

An array that's used for more than its length is fine, and so is a longer separator:

example.jsNo problems

const lines = source.split("\n");
console.log(lines.length, lines[0]);

const paragraphCount = source.split("\n\n").length;

Options#

Option	Default	What it does
`countFunction`	none	The name of a function that's called as `countFunction(string, separator)` and returns how often the separator occurs.

Without countFunction, the rule only reports. With it, --fix rewrites source.split("\n").length to count(source, "\n") + 1, and source.split("\n").length - 1 to count(source, "\n"). The fix only applies where a function with that name is in scope.

bunfig.toml

[lint.rules]
"bun/no-array-just-to-count" = ["error", { countFunction = "count" }]

example.jswith { "countFunction": "count" }1 problem

import { count } from "./strings.js";

const commas = row.split(",").length - 1;