↑
Main Page

apply() method

The apply() method

The

apply()

method takes two arguments: the object to be used for

this

and an array of arguments to

be passed to the function. For example:

function sayColor(sPrefix, sSuffix) {

alert(sPrefix + this.color + sSuffix);

};

var obj = new Object();

obj.color = “red”;

//outputs “The color is red, a very nice color indeed. “

sayColor.apply(obj, new Array(“The color is “,”, a very nice color indeed.”));

This is the same example as before, but now the

apply()

method is being called. When

apply()

called, the first argument is still

obj

, which indicates that the

this

keyword in

sayColor()

should be

assigned the value of

obj

. The second argument is an array consisting of two strings, which are matched

up with the

prefix

and

suffix

arguments of

sayColor()

. This also results in the message

“The color

is red, a very nice color indeed.”

being displayed.

This method is also used in place of the three lines to assign, call, and delete the new method:

function ClassB(sColor, sName) {

//this.newMethod = ClassA;

//this.newMethod(sColor);

//delete this.newMethod;

ClassA.apply(this, new Array(sColor));

this.name = sName;

this.sayName = function () {

alert(this.name);

};

}

Once again, you pass

this

in as the first argument. The second argument is an array with just one value:

color

. You can, alternatively, pass in the entire

arguments

object of

ClassB

as the second argument of

the

apply()

method:

function ClassB(sColor, sName) {

//this.newMethod = ClassA;

//this.newMethod(sColor);

//delete this.newMethod;

ClassA.apply(this, arguments);

this.name = sName;

this.sayName = function () {

alert(this.name);

};

}

Of course, passing in the object of the arguments only works if the order of the arguments in the super-

class constructor is exactly the same as the order of the arguments in the subclass. When this is not the

108

Chapter 4

07_579088 ch04.qxd 3/28/05 11:36 AM Page 108