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Very late binding

You may recall from Chapter 2 that the

Function

’s

toString()

method normally outputs the source

code of the function. By overriding that method, you can supply a different string to return (in this case,

“Function code hidden”

). But what happened to the original function that

toString()

was point-

ing to? Well, it has gone on to the garbage collector because it was fully dereferenced. You have no way

to get that original function back, which is why it is always safer to store a pointer to the original method

that you are overriding, just in case you need it later. You may even want to call that original method

under certain circumstances in your new method:

Function.prototype.originalToString = Function.prototype.toString;

Function.prototype.toString = function () {

if (this.originalToString().length > 100) {

return “Function too long to display.”;

} else {

return this.originalToString();

}

};

In this code, the first line saves a reference to the current

toString()

method in a property called

originalToString

. Then, the

toString()

method is overridden with a custom method. This new

method checks to see if the length of the function source code is longer greater than 100. If so, the

method returns a small error message stating that the function code is too long; otherwise, it returns

the source code by calling

originalToString()

Very late binding

Technically speaking, there is no such thing as very late binding. The term is used in this book to describe

a phenomenon in ECMAScript where it is possible to define a method for a type of object after the object

has already been instantiated. For example:

var o = new Object;

Object.prototype.sayHi = function () {

alert(“hi”);

};

o.sayHi();

In most programming languages, you must define object methods well in advance of object instantia-

tion. Here, the

sayHi()

method is added to the

Object

class after an instance has been created. Not

only is that unheard of in traditional languages, but the instance of

Object

is then automatically

assigned the method and it can be used immediately (on the following line).

It is not recommended that you use very late binding because it can be difficult to

keep track of and document. However, you should understand that it is possible.

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Object Basics

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