SyntaxError: label not found

The JavaScript exception "label not found" occurs when a break or continue statement references a label that does not exist on any statement that contains the break or continue statement.

Message

SyntaxError: Undefined label 'label' (V8-based)
SyntaxError: label not found (Firefox)
SyntaxError: Cannot use the undeclared label 'label'. (Safari)

Error type

SyntaxError.

What went wrong?

In JavaScript, labels are very limited: you can only use them with break and continue statements, and you can only jump to them from a statement contained within the labeled statement. You cannot jump to this label from anywhere in the program.

Examples

Unsyntactic jump

You cannot use labels as if they are goto.

js

start: console.log("Hello, world!");
console.log("Do it again");
break start;

Instead, you can only use labels to enhance the normal semantics of break and continue statements.

js

start: {
  console.log("Hello, world!");
  if (Math.random() > 0.5) {
    break start;
  }
  console.log("Maybe I'm logged");
}

See also