#no-unreachable-loop

#Configuration

import { defineConfig, js } from '@rslint/core';

export default defineConfig([
  js.configs.recommended,
  {
    rules: {
      'no-unreachable-loop': 'error',
    },
  },
]);

#Rule Details

Disallows a loop whose body can never run a second time. Every path through the body leaves the loop — by break, return, or throw — so the loop is a conditional block written as a loop, and the extra iterations it looks like it performs never happen. That is usually a mistake: a break that belongs inside an if, a return that should collect results instead of leaving on the first element, or a condition that was never finished.

A loop iterates again as soon as one path flows back into it, so a break or return guarded by an if is fine. A loop the surrounding code can never reach is left alone.

Examples of incorrect code for this rule:

for (let i = 0; i < arr.length; i++) {
  console.log(arr[i]);
  break;
}

while (foo) {
  doSomething(foo);
  foo = foo.parent;
  return;
}

function find(arr, target) {
  for (const item of arr) {
    return item === target;
  }
}

Examples of correct code for this rule:

for (let i = 0; i < arr.length; i++) {
  console.log(arr[i]);
}

while (foo) {
  if (bar) {
    break;
  }
  foo = foo.parent;
}

function find(arr, target) {
  for (const item of arr) {
    if (item === target) {
      return item;
    }
  }
}

#Options

This rule accepts an options object with one property:

#ignore

An array of loop types to leave unchecked. Each entry is one of "WhileStatement", "DoWhileStatement", "ForStatement", "ForInStatement", or "ForOfStatement". It defaults to an empty array.

The following configuration allows the idiom that reads only the first entry of a collection:

{
  "no-unreachable-loop": [
    "error",
    { "ignore": ["ForInStatement", "ForOfStatement"] }
  ]
}

function firstKey(obj) {
  for (const key in obj) {
    return key;
  }
  return null;
}

#Differences from ESLint

• rslint accepts double-labelled while and do-while loops when continue targets the outer label. ESLint 10.8.0 reports those two forms even though the jump starts another iteration.
• rslint accepts an enclosing loop when continue in a finally block overrides a pending return or throw. ESLint 10.8.0 reports some of these code paths even though control starts another iteration.

#Original Documentation

• ESLint no-unreachable-loop