Availability

Navigator 3.0

Description

The constructor property of any object is a read-only 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, then a.constructor will be 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 a Document object:

function isDocument(x) { 
    return ((typeof x == "object") && (x.constructor == "Document"));
}

See Also

"Object", Chapter 7, Objects