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
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.
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");
}