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BOOK: Professional JavaScript for Web Developers ISBN: 978-0-7645-7908-0
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Old October 26th, 2009, 03:24 AM
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Default Chapter 3 - StringBuffer vs += Performance Issue

I have just copied down the code for the StringBuffer "class" performance comparison on pgs 97-98 of the book but my results are opposite to what the book is explaining. The += operation without using the StringBuffer class is actually running significantly faster. Here is the code:

Code:
function StringBuffer1() {
	this._strings = new Array;

	if (typeof StringBuffer1._initialized == "undefined") {
		StringBuffer1.prototype.append = function (str) {
			this._strings.push(str)
		};
		StringBuffer1.prototype.toString = function () {
			return this._strings.join("");
		};
		StringBuffer1._initialized = true;
	};
};

function StringBuffer2() {
	this._strings = new Array;
};
StringBuffer2.prototype.append = function (str) {
	this._strings.push(str)
};
StringBuffer2.prototype.toString = function () {
	return this._strings.join("");
};




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<br />");

var oBuffer = new StringBuffer1();
d1 = new Date();
for (var i=0; i < 10000; i++) {
	oBuffer.append("text");
}
var sResult = oBuffer.toString();
d2 = new Date();
document.write("Concatenation with StringBuffer1: " + (d2.getTime() - d1.getTime()) + " milliseconds<br />");

var oBuffer = new StringBuffer2();
d1 = new Date();
for (var i=0; i < 10000; i++) {
	oBuffer.append("text");
}
var sResult = oBuffer.toString();
d2 = new Date();
document.write("Concatenation with StringBuffer2: " + (d2.getTime() - d1.getTime()) + " milliseconds<br />");
results:
Concatenation with plus: 12 milliseconds
Concatenation with StringBuffer1: 23 milliseconds
Concatenation with StringBuffer2: 26 milliseconds

I do have the 2005 version of the text, so I don't know if something has been changed with javascript since this publication. I'm also using Firefox 3.0.14 right now.

Last edited by IAmCorbin; October 26th, 2009 at 03:27 AM..





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