label

Labeled statements basics

a label is a (non-reserved) word followed by a colon

nonReservedWord; { break nonReservedWord; } assert(true);

WHEN prefixing a block with a label THEN break label stops execution of this block

label: { break; assert(false, 'This should never be reached'); } assert(true);

GIVEN a nested loop WHEN breaking the most inner loop THEN both loops stop

let count = 0; outer-label: for (let i = 0; i < 3; i++) { for (let j = 0; j < 3; j++) { count++; break outer; } } assert.deepEqual(count, 1);

GIVEN a nested loop WHEN calling continue label inside THEN the inner loop is skipped

let hits = []; outer: for (let i = 0; i < 2; i++) { for (let j = 0; j < 2; j++) { if (j === 1) { break outer; } hits.push([i, j]); } } assert.deepEqual(hits, [[0, 0], [1, 0]]);

some fun

an unused label: is fine, valid but useless JS

label assert(true);

a URL is valid code 😮

http s://jskatas.org assert(true);

Links

mdn docs Very well readable, easy to understand description of how labels works.
spec The version of the specification where labels were introduced, see section 12.12. (PDF 723kB)
article Labeled statements - the forgotten JS feature – Filip

Required Knowledge

`let` declaration (Block scope)

Related Katas

label basics

Difficulty Level

INTERMEDIATE

First Published

26 November 2025

Stats

6 tests to solve