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label

The labeled statement can be used with break or continue statements. It is prefixing a statement with an identifier which you can refer to.

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Syntax

label:
  statement

label: Any JavaScript identifier that is not a reserved word.
statement: A JavaScript statement. break can be used with any labeled statement, and continue can be used with looping labeled statements.

Description

You can use a label to identify a loop, and then use the break or continue statements to indicate whether a program should interrupt the loop or continue its execution.

Note that JavaScript has no goto statement, you can only use labels with break or continue.

In strict mode code, you can't use let as a label name. It will throw a SyntaxError (let is a reserved identifier).

Examples

Using a labeled continue with for loops

let i, j;

loop1:
for (i = 0; i < 3; i++) {      //The first for statement is labeled "loop1"
  loop2:
  for (j = 0; j < 3; j++) {   //The second for statement is labeled "loop2"
    if (i === 1 && j === 1) {
      continue loop1;
    }
    console.log(`i = ${i}, j = ${j}`);
  }
}

// Output is:
//   "i = 0, j = 0"
//   "i = 0, j = 1"
//   "i = 0, j = 2"
//   "i = 1, j = 0"
//   "i = 2, j = 0"
//   "i = 2, j = 1"
//   "i = 2, j = 2"
// Notice how it skips both "i = 1, j = 1" and "i = 1, j = 2"

Using a labeled continue statement

Given an array of items and an array of tests, this example counts the number of items that passes all the tests.

let itemsPassed = 0;
let i, j;

top:
for (i = 0; i < items.length; i++) {
  for (j = 0; j < tests.length; j++) {
    if (!tests[j].pass(items[i])) {
      continue top;
    }
  }

  itemsPassed++;
}

Using a labeled break with for loops

let i, j;

loop1:
for (i = 0; i < 3; i++) {      //The first for statement is labeled "loop1"
  loop2:
  for (j = 0; j < 3; j++) {   //The second for statement is labeled "loop2"
    if (i === 1 && j === 1) {
      break loop1;
    }
    console.log(`i = ${i}, j = ${j}`);
  }
}

// Output is:
//   "i = 0, j = 0"
//   "i = 0, j = 1"
//   "i = 0, j = 2"
//   "i = 1, j = 0"
// Notice the difference with the previous continue example

Using a labeled break statement

Given an array of items and an array of tests, this example determines whether all items pass all tests.

let allPass = true;
let i, j;

top:
for (i = 0; i < items.length; i++) {
  for (j = 0; j < tests.length; j++) {
    if (!tests[j].pass(items[i])) {
      allPass = false;
      break top;
    }
  }
}

Using a labeled block with break

You can use labels within simple blocks, but only break statements can make use of non-loop labels.

foo: {
  console.log('face');
  break foo;
  console.log('this will not be executed');
}
console.log('swap');

// this will log:

// "face"
// "swap"

Labeled function declarations

Labels can only be applied to statements, not declarations. Still, the Annex B: Additional ECMAScript Features for Web Browsers section defines a legacy grammar to standardize labeled function declarations in non-strict code.

L: function F() {}

In strict mode code, however, this will throw a SyntaxError:

'use strict';
L: function F() {}
// SyntaxError: functions cannot be labelled

Generator functions can neither be labeled in strict code, nor in non-strict code:

L: function* F() {}
// SyntaxError: generator functions cannot be labelled

Specifications

Specification
ECMAScript Language Specification # sec-labelled-statements

Browser compatibility

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	Deno	Node.js
`label`	1	12	1	4	4	1	4.4	18	4	10.1	1	1.0	1.0	0.10.0