Section 24.141. Object.constructor: an object s constructor function


24.141. Object.constructor: an object's constructor function

ECMAScript v1

24.141.1. Synopsis

object.constructor

24.141.2. Description

The constructor property of any object is a reference to the function that was used as the constructor for that object. For example, if you create an array a with the Array( ) constructor, a.constructor is an Array:

 a = new Array(1,2,3);   // Create an object a.constructor == Array  // Evaluates to true 

One common use of the constructor property is to determine the type of unknown objects. Given an unknown value, you can use the typeof operator to determine whether it is a primitive value or an object. If it is an object, you can use the constructor property to determine what type of object it is. For example, the following function determines whether a given value is an array:

 function isArray(x) {     return ((typeof x == "object") && (x.constructor == Array)); } 

Note, however, that while this technique works for the objects built into core JavaScript, it is not guaranteed to work with host objects such as the Window object of client-side JavaScript. The default implementation of the Object.toString( ) method provides another way to determine the type of an unknown object.

24.141.3. See Also

 Object.toString( ) 




JavaScript. The Definitive Guide
JavaScript: The Definitive Guide
ISBN: 0596101996
EAN: 2147483647
Year: 2004
Pages: 767

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net