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

SyntaxError.

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.

You cannot use labels as if they are goto.

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.

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

• Labeled statement