ECMA-262 Core: JavaScript Undefined Data Type

Navigation Aids -- This Page        Navigation Aids -- This Topic        Navigation Aids -- This Site

Introduction And Review

The ECMA-262 standard defines the term Undefined Type as: the type Undefined has the value called undefined.

The Undefined data type is one of five ECMAScript primitive types. The other four are: Number, Boolean, Null and String. All primitive types have a definite (fixed) size except for the String type.

The Undefined type is distinguished from other types using a dynamic or weak typing method. The method involves interrogating the value token. A variable that is declared but uninitialized is given the Undefined type with a value of "undefined". Also, an object property that does not exist will return the undefined value.

Undefined Types


Rx4AJAX        About Us | Topic Index | Contact Us | Privacy Policy | 2008 This Site Built By PPThompson