switch...case语句与if...else性能比较 -- JavaScript教程

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<html>
	<head>
		<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
		<title>switch...case语句与if...else性能比较</title>		<script type="text/javascript">
		//声明一点，switch语句只能比较常量，而if语句可以比较复杂的表达式
		//可以通过几个常用的浏览器测试，会得到不同的结果
		
		var count=99999;
		
		function nIfElseTest(num)
		{
			var dBegin=new Date;
			//进行
		
			var iNum=0;
			for(var i=0;i<count;i++)
			{
				if(num==0)
				{
					iNum=0;
				}
				else if(num==1)
				{
					iNum=0;
				}
				else if(num==2)
				{
					iNum=0;
				}
				else if(num==3)
				{
					iNum=0;
				}
				else if(num==4)
				{
					iNum=0;
				}
				else if(num==5)
				{
					iNum=0;
				}
				else if(num==6)
				{
					iNum=0;
				}
				else if(num==7)
				{
					iNum=0;
				}
				else if(num==8)
				{
					iNum=0;
				}
				else if(num==9)
				{
					iNum=0;
				}
				else if(num==10)
				{
					iNum=0;
				}
				else if(num==11)
				{
					iNum=0;
				}
				else if(num==12)
				{
					iNum=0;
				}
				else if(num==13)
				{
					iNum=0;
				}
				else if(num==14)
				{
					iNum=0;
				}
				else if(num==15)
				{
					iNum=0;
				}
				else if(num==16)
				{
					iNum=0;
				}
				else if(num==17)
				{
					iNum=0;
				}
				else if(num==18)
				{
					iNum=0;
				}
			}
			var dEnd=new Date;
			document.write("if...else耗时"+(dEnd.getTime()-dBegin.getTime())+"毫秒"+",num="+num+"<a href='javascript:history.back()'>继续测试</a>");
		}
		
		function nSwitchCaseTest(num)
		{
			var dBegin=new Date;
			//进行
			for(var i=0;i<count;i++)
			{
				switch(num)
				{
					case 0: 
						iNum=0;break;
					case 1: 
						iNum=0;break;
					case 2: 
						iNum=0;break;
					case 3: 
						iNum=0;break;
					case 4: 
						iNum=0;break;
					case 5: 
						iNum=0;break;
					case 6: 
						iNum=0;break;
					case 7: 
						iNum=0;break;
					case 8: 
						iNum=0;break;
					case 9: 
						iNum=0;break;
					case 10: 
						iNum=0;break;
					case 11: 
						iNum=0;break;
					case 12: 
						iNum=0;break;
					case 13: 
						iNum=0;break;
					case 14: 
						iNum=0;break;
					case 15: 
						iNum=0;break;
					case 16: 
						iNum=0;break;
					case 17: 
						iNum=0;break;
					case 18: 
						iNum=0;break;
					default:
				}
			}
			var dEnd=new Date;
			document.write("switch_case耗时"+(dEnd.getTime()-dBegin.getTime())+"毫秒"+",num="+num+"<a href='javascript:history.back()'>继续测试</a>");
		}
		</script>
	</head>
	<body>
		<button onClick="javaScript:nIfElseTest(0)">if0</button> 
		<button onClick="javaScript:nIfElseTest(2)">if2</button> 
		<button onClick="javaScript:nIfElseTest(4)">if4</button> 
		<button onClick="javaScript:nIfElseTest(6)">if6</button> 
		<button onClick="javaScript:nIfElseTest(8)">if8</button> 
		<button onClick="javaScript:nIfElseTest(10)">if10</button> 
		<button onClick="javaScript:nIfElseTest(12)">if12</button> 
		<button onClick="javaScript:nIfElseTest(14)">if14</button> 
		<button onClick="javaScript:nIfElseTest(16)">if16</button> 
		<button onClick="javaScript:nIfElseTest(18)">if18</button>
		
		<p><a href="http://www.dreamdu.com/javascript/switch_case/">switch...case</a>测试</p>
		
		<button onClick="javaScript:nSwitchCaseTest(0)">switch0</button>
		<button onClick="javaScript:nSwitchCaseTest(2)">switch2</button>
		<button onClick="javaScript:nSwitchCaseTest(4)">switch4</button>
		<button onClick="javaScript:nSwitchCaseTest(6)">switch6</button>
		<button onClick="javaScript:nSwitchCaseTest(8)">switch8</button>
		<button onClick="javaScript:nSwitchCaseTest(10)">switch10</button>
		<button onClick="javaScript:nSwitchCaseTest(12)">switch12</button>
		<button onClick="javaScript:nSwitchCaseTest(14)">switch14</button>
		<button onClick="javaScript:nSwitchCaseTest(16)">switch16</button>
		<button onClick="javaScript:nSwitchCaseTest(18)">switch18</button>

</body>
</html>