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