SyntaxError: unlabeled break must be inside loop or switch
The JavaScript exception "unlabeled break must be inside loop or switch" occurs when a break statement is not inside a loop or a 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?
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 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 forEach() loop. You can use some() instead, or convert it to a 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
}