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5.6.1 Labeled Statements

5.6.1 Labeled Statements


Any statement may be labeled by preceding it with an identifier and a colon:

identifier: statement

By labeling a statement, you give it a name that you can use to refer to it elsewhere in your program. You can label any statement, although it is only useful to label statements that have bodies, such as loops and conditionals. By giving a loop a name, you can use break and continue statements inside the body of the loop to exit the loop or to jump directly to the top of the loop to begin the next iteration. break and continue are the only JavaScript statements that use statement labels; they are covered later in this chapter. Here is an example of a labeled while loop and a continue statement that uses the label.

mainloop: while(token != null) {

// Code omitted...

continue mainloop; // Jump to the next iteration of the named loop

// More code omitted...

}

The identifier you use to label a statement can be any legal JavaScript identifier that is not a reserved word. The namespace for labels is different than the namespace for variables and functions, so you can use the same identifier as a statement label and as a variable or function name. Statement labels are defined only within the statement to which they apply (and within its substatements, of course). A statement may not have the same label as a statement that contains it, but two statements may have the same label as long as neither one is nested within the other. Labeled statements may themselves be labeled. Effectively, this means that any statement may have multiple labels.

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