Microsoft® JScript™ prototype Property |
Language Reference Version 2 |
Contains a reference to the prototype for a class of objects.
objectname.prototypeThe objectname argument is the name of an object.
Use the prototype property to provide a base set of functionality to a class of objects. New instances of an object "inherit" the behavior of the prototype assigned to that object.For example, say you wanted to add a method to the Array object that returns the value of the largest element of the array. To do this, declare the function, add it to Array.prototype, and then use it.
After this code is executed, y contains the largest value in the array x, or 6.function array_max( ) { var i, max = this[0]; for (i = 1; i < this.length; i++) { if (max < this[i]) max = this[i]; } } Array.prototype.max = array_max; var x = new Array(1, 2, 3, 4, 5, 6); var y = x.max( );All intrinsic JScript objects have a prototype property that is read-only. Functionality may be added to the prototype, as in the example, but the object may not be assigned a different prototype.
This is not the case for user-defined objects: User-defined objects may be assigned a new prototype.
The method and property lists for each intrinsic object in this language reference indicate which ones are part of the object's prototype, and which are not.
© 1997 by Microsoft Corporation. All rights reserved.
More documentation and examples from Netscape. :
function Car(make, model, year) {
this.make = make
this.model = model
this.year = year
}
var myCar = new Car("Acura", "Integra", 1987)
Car.prototype.wheels = 4 // no 3-wheelers please!
if (myCar.wheels == 4)
document.write("The car myCar has ", myCar.wheels, " wheels.")
var s1 = new String("a")
var s2 = new String("b")
var s3 = new String("c")
// Create a repeat-string-N-times method for all String objects
function str_rep(n) {
var s = "", t = this.toString()
while (--n >= 0) s += t
return s
}
String.prototype.rep = str_rep
// Display the results
document.write("<P>s1.rep(3) is " + s1.rep(3)) // "aaa"
document.write("<BR>s2.rep(5) is " + s2.rep(5)) // "bbbbb"
document.write("<BR>s3.rep(2) is " + s3.rep(2)) // "cc"
// Create an alternate method and assign it to only one String variable
function fake_rep(n) {
return "repeat " + this + n + " times."
}
s1.rep = fake_rep
document.write("<P>s1.rep(1) is " + s1.rep(1)) // "repeat a 1 times."
document.write("<BR>s2.rep(4) is " + s2.rep(4)) // "bbbb"
document.write("<BR>s3.rep(6) is " + s3.rep(6)) // "cccccc"
This example produces the following output:
s1.rep(3) is aaa
s2.rep(5) is bbbbb
s3.rep(2) is cc
s1.rep(1) is repeat a1 times.
s2.rep(4) is bbbb
s3.rep(6) is cccccc
"z".rep(3)+
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