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SyntaxError: unlabeled break must be inside loop or switch

The JavaScript exception "unlabeled break must be inside loop or switch" occurs when a {{jsxref("Statements/break", "break")}} statement is not inside a loop or a {{jsxref("Statements/switch", "switch")}} statement.

Message

SyntaxError: Illegal break statement (V8-based)
SyntaxError: unlabeled break must be inside loop or switch (Firefox)
SyntaxError: 'break' is only valid inside a switch or loop statement. (Safari)

Error type

.

What went wrong?

{{jsxref("Statements/break", "break")}} statements can be used to exit a loop or a switch statement, and using them elsewhere is a syntax error. Alternatively, you can provide a label to the break statement to break out of any statement with that label — however, if the label does not reference a containing statement, another error SyntaxError: label not found will be thrown.

Examples

Unsyntactic break

break cannot be used outside switch or loops.

let score = 0;

function increment() {
if (score === 100)
break; // SyntaxError: unlabeled break must be inside loop or switch
}
score++;
}

Maybe instead of break, you intend to use {{jsxref("Statements/return", "return")}} to early-terminate a function.

let score = 0;

function increment() {
if (score === 100) {
return;
}
score++;
}

Using break in callbacks

break cannot be used in callbacks, even if the callback is called from a loop.

let containingIndex = 0;
const matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9],
];

while (containingIndex < matrix.length) {
matrix[containingIndex].forEach((value) => {
if (value === 5) {
break; // SyntaxError: unlabeled break must be inside loop or switch
}
});
containingIndex++;
}

Instead, refactor the code so the break is used outside the callback.

let containingIndex = 0;
const matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9],
];

outer: while (containingIndex < matrix.length) {
for (const value of matrix[containingIndex]) {
if (value === 5) {
break outer;
}
}
containingIndex++;
}
let containingIndex = 0;
const matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9],
];

while (containingIndex < matrix.length) {
if (matrix[containingIndex].includes(5)) {
break;
}
containingIndex++;
}

There's no way to early-terminate a {{jsxref("Array/forEach", "forEach()")}} loop. You can use {{jsxref("Array/some", "some()")}} instead, or convert it to a {{jsxref("Statements/for...of", "for...of")}} loop.

array.forEach((value) => {
if (value === 5) {
break; // SyntaxError: unlabeled break must be inside loop or switch
}
// do something with value
});
array.some((value) => {
if (value === 5) {
return true;
}
// do something with value
return false;
});
for (const value of array) {
if (value === 5) {
break;
}
// do something with value
}

See also

  • {{jsxref("Statements/break", "break")}}