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;

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

// Logs:
// 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;

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

// Logs:
// 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

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See also