Pure JavaScript

typeof

JavaScript1.1+, JScript1.0+ NES2+, Nav3+, IE3+, Opera3+ Syntax

typeof(variable)

Description

The typeof unary operator is used to determine the type of the variable passed to it. The return values of this operator are boolean, number, object, string, or undefined.

Note

Because undefined was not fully implemented until JavaScript 1.3 and JScript 3.0, many supporting browsers return null when passing a variable that has not been defined.

Example

Listing 6.267 creates boolean, number, object, string, and undefined variable instances, and then uses the typeof operator to write their type to the page.

Listing 6.267 This Example Uses the typeof Unary Operator to Return the Types for Four Different Variables

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