JavaScript: The Definitive Guide, Fourth Edition

break

The break statement causes the innermost enclosing loop or a switch statement to exit immediately. Its syntax is simple:

break;

Because it causes a loop or switch to exit, this form of the break statement is legal only if it appears within one of these statements.

ECMAScript v3 and JavaScript 1.2 allow the break keyword to be followed by the name of a label:

break labelname;

Note that labelname is simply an identifier; it is not followed by a colon, as it would be when defining a labeled statement.

When break is used with a label, it jumps to the end of, or terminates, the named statement, which may be any enclosing statement. The named statement need not be a loop or switch; a break statement used with a label need not even be contained within a loop or switch. The only restriction on the label of the break statement is that it name an enclosing statement. The label can name an if statement, for example, or even a block of statements grouped within curly braces, for the sole purpose of naming the block with a label.

As discussed in Chapter 2, a newline is not allowed between the break keyword and the labelname. This is an oddity of JavaScript syntax caused by its automatic insertion of omitted semicolons. If you break a line of code between the break keyword and the following label, JavaScript assumes you meant to use the simple, unlabeled form of the statement and adds a semicolon for you.

We’ve already seen examples of the break statement within a switch statement. ...