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Redefining an existing method

}

return -1;

}

This method, named

indexOf()

to keep it consistent with the

String

method of the same name,

searches each item in the array until it finds the equivalent of the item passed in. If the item is found,

the method returns the position; if not, the method returns

–1

. With this defined, the following code is

possible:

var aColors = new Array(“red”, “green”, “yellow”);

alert(aColors.indexOf(“green”)); //outputs “1”

Lastly, if you want to add a new method to every native object in ECMAScript, you must define it on the

Object

’s prototype property. As discussed in the last chapter, all native objects inherit from

Object

, and

so any changes to

Object

are reflected in all native objects. For example, if you want to add a method

that outputs the current value of the object in an alert, you do the following:

Object.prototype.showValue = function () {

alert(this.valueOf());

};

var str = “hello”;

var iNum = 25;

str.showValue(); //outputs “hello”

iNum.showValue(); //outputs “25”

Here, both the

String

and

Number

objects inherit the

showValue()

method from

Object

, displaying

“hello”

and

“25”

when called on their respective objects.

Redefining an existing method

Just as it is possible to define new methods for existing classes, it is also possible to redefine existing

methods. As discussed in the previous chapter, function names are simply pointers to functions, and as

such, can be easily changed to point to other functions. What happens if you change a native method,

such as

toString()

Function.prototype.toString = function () {

return “Function code hidden”;

};

The previous code is perfectly legal and works as expected:

function sayHi() {

alert(“hi”);

}

alert(sayHi.toString()); //outputs “Function code hidden”

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