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practical example

Which one to use?

As mentioned previously, the hybrid constructor/prototype paradigm is the one most widely used at

present. That being said, dynamic prototyping is catching on in popularity and is functionally equiva-

lent. Using either of these two methods is perfectly fine. Don’t ever get caught using the classic, con-

structor or prototype paradigms alone, however, because you may introduce problems into code.

A practical example

Part of the appeal of objects is the way they can be used to solve problems. One of the common problems

in ECMAScript is the performance of string concatenation. Similar to other languages, ECMAScript

strings are

immutable

, meaning that their value cannot be changed. Consider the following code:

var str = “hello “;

str += “world”;

This code actually executes the following steps behind the scenes:

Create a string to store

“hello “

Create a string to store

“world”

Create a string to store the result of concatenation.

Copy the current contents of

str

into the result.

Copy the

“world”

into the result.

Update

str

to point to the result.

Steps 2–6 occur every time a string concatenation is completed, making this a very expensive operation.

If this process is repeated hundreds or even thousands of times, performance suffers. The solution is to

use an

Array

object to store the strings and then use the

join()

method (with an empty string as an

argument) to create the final string. Imagine writing this code instead:

var arr = new Array;

arr[0] = “hello “;

arr[1] = “world”;

var str = arr.join(“”);

Using this method, it doesn’t matter how many strings are introduced into the array because the only

concatenation occurs when the

join()

method is called. At that point, the following steps are executed:

Create a string to store the result.

Copy each string into the appropriate spot in the result.

Although this solution is good, it could be better. The problem is that the code doesn’t accurately reflect

its intent. To make it more understandable, this functionality can be wrapped in a

StringBuffer

class:

function StringBuffer() {

this.__strings__ = new Array;

}

Object Basics

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