Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

Availability

JavaScript 1.1; JScript 2.0; ECMAScript v1

Synopsis

object.constructor

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-in to 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.

See Also

Object.toString( )