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traditional string concatenation

StringBuffer.prototype.append = function (str) {

this.__strings__.push(str);

};

StringBuffer.prototype.toString = function () {

return this.__strings__.join(“”);

};

The first thing to note about this code is the

strings

property, which is intended to be private. It has

only two methods:

append()

and

toString()

. The

append()

method takes an argument and appends

it to the strings array and the

toString()

method returns the actual concatenated string by using the

array’s

join()

method. To concatenate a group of strings using a

StringBuffer

object, use the follow-

ing code:

var buffer = new StringBuffer();

buffer.append(“hello “);

buffer.append(“world”);

var result = buffer.toString();

You can test the performance of the

StringBuffer

object versus traditional string concatenation with

the following code:

var d1 = new Date();

var str = “”;

for (var i=0; i < 10000; i++) {

str += “text”;

}

var d2 = new Date();

document.write(“Concatenation with plus: “ + (d2.getTime() - d1.getTime()) + “

milliseconds”);

var oBuffer = new StringBuffer();

d1 = new Date();

for (var i=0; i < 10000; i++) {

oBuffer.append(“text”);

}

var sResult = buffer.toString();

d2 = new Date();

document.write(“<br />Concatenation with StringBuffer: “ + (d2.getTime() -

d1.getTime()) + “ milliseconds”);

The code runs two tests on string concatenation, the first by using the additive operator and the second

by using the

StringBuffer

. Each operation concatenates 10,000 strings. The dates

and

are used

to determine how much time it takes to complete the operation. Remember, when you create a new

Date

object without any arguments, it is assigned current date and time. To figure out how much time elapsed

during the concatenation, the millisecond representation of the dates (returned by the

getTime()

method) are subtracted. This is a common method of measuring JavaScript performance. The results of

this test should show a savings of 100–200% over using the additive operator.

Chapter 3

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