files/en-us/web/javascript/reference/errors/bad_break/index.md

metadata

title: 'SyntaxError: unlabeled break must be inside loop or switch'
slug: Web/JavaScript/Reference/Errors/Bad_break
page-type: javascript-error
sidebar: jssidebar

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

{{jsxref("SyntaxError")}}.

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")}}