javascript程序的执行效率问题

写了几年代码，很少谈到javascript程序的执行效率问题，今天就举几个例子看看，让大家看看程序优化是多么重要。
这节来看看createElement和innerHTML的表现。看看差别是多大

createElement:

运行代码框
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <TITLE> New Document </TITLE> <META NAME="Generator" CONTENT="EditPlus"> <META NAME="Author" CONTENT=""> <META NAME="Keywords" CONTENT=""> <META NAME="Description" CONTENT=""> <script type="text/javascript"> function init(){ var staDate = new Date(); var doc = window.document; for(var i=0;i<100;i++){ var oDiv = doc.createElement("div"); var oText = doc.createTextNode("text"); oDiv.appendChild(oText); container.appendChild(oDiv); oDiv.style.id = "div_"+i; oDiv.style.width = "100px"; oDiv.style.height = "20px"; oDiv.style.backgroundColor = "#eee"; } alert(new Date - staDate); } </script> </HEAD> <BODY> <div id="container"></div> <input type="button" value="start" onclick="init();" /> </BODY> </HTML>
[Ctrl+A 全部选择提示：你可先修改部分代码，再按运行]

innerHTML:

第二讲：同样是createNode，再来看看执行顺序的差别

先创建子节点，再append到父节点：

运行代码框
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <TITLE> New Document </TITLE> <META NAME="Generator" CONTENT="EditPlus"> <META NAME="Author" CONTENT=""> <META NAME="Keywords" CONTENT=""> <META NAME="Description" CONTENT=""> <script type="text/javascript"> function init(){ var staDate = new Date(); var doc = window.document; for(var i=0;i<100;i++){ var oDiv = doc.createElement("div"); var oTab = doc.createElement("table"); var oTbody = doc.createElement("tbody"); var oTr = doc.createElement("tr"); var oTd = doc.createElement("td"); var oText = doc.createTextNode("毛主席向全世界宣布：中华人民共和国从此成立了"); oTd.appendChild(oText); oTr.appendChild(oTd); oTbody.appendChild(oTr); oTab.appendChild(oTbody); oDiv.appendChild(oTab); container.appendChild(oDiv); oDiv.id = "div_"+i; oDiv.style.width = "400px"; oDiv.style.height = "20px"; oDiv.style.backgroundColor = "#eee"; } //alert(container.innerHTML); alert(new Date - staDate); } </script> </HEAD> <BODY> <div id="container"></div> <input type="button" value="start" onclick="init();" /> </BODY> </HTML>
[Ctrl+A 全部选择提示：你可先修改部分代码，再按运行]

先append到父节点，再创建子节点：

运行代码框
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <TITLE> New Document </TITLE> <META NAME="Generator" CONTENT="EditPlus"> <META NAME="Author" CONTENT=""> <META NAME="Keywords" CONTENT=""> <META NAME="Description" CONTENT=""> <script type="text/javascript"> function init(){ var staDate = new Date(); var doc = window.document; for(var i=0;i<100;i++){ var oDiv = doc.createElement("div"); var oTab = doc.createElement("table"); var oTbody = doc.createElement("tbody"); var oTr = doc.createElement("tr"); var oTd = doc.createElement("td"); var oText = doc.createTextNode("毛主席向全世界宣布：中华人民共和国从此成立了"); container.appendChild(oDiv); oDiv.appendChild(oTab); oTab.appendChild(oTbody); oTbody.appendChild(oTr); oTr.appendChild(oTd); oTd.appendChild(oText); oDiv.id = "div_"+i; oDiv.style.width = "400px"; oDiv.style.height = "20px"; oDiv.style.backgroundColor = "#eee"; } //alert(container.innerHTML); alert(new Date - staDate); } </script> </HEAD> <BODY> <div id="container"></div> <input type="button" value="start" onclick="init();" /> </BODY> </HTML>
[Ctrl+A 全部选择提示：你可先修改部分代码，再按运行]

运行代码框

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<script type="text/javascript">
function init(){
var staDate = new Date();
var doc = window.document;
for(var i=0;i<100;i++){
if(container.childNodes.length>0){
var oDiv = container.lastChild.cloneNode(true);
oDiv.id="div_"+i;
container.appendChild(oDiv);
}else{
var oDiv = doc.createElement("div");
var oTab  = doc.createElement("table");
var oTbody  = doc.createElement("tbody");
var oTr = doc.createElement("tr");
var oTd = doc.createElement("td");
var oText = doc.createTextNode("毛主席向全世界宣布：中华人民共和国从此成立了");
container.appendChild(oDiv);
oDiv.appendChild(oTab);
oTab.appendChild(oTbody);
oTbody.appendChild(oTr);
oTr.appendChild(oTd);
oTd.appendChild(oText);
oDiv.id = "div_"+i;
oDiv.style.width = "400px";
oDiv.style.height = "20px";
oDiv.style.backgroundColor = "#eee";
}
}
//alert(container.innerHTML);
alert(new Date - staDate);
}
</script>
</HEAD>
<BODY>
<div id="container"></div>
<input type="button" value="start" onclick="init();" />
</BODY>
</HTML>

[Ctrl+A 全部选择提示：你可先修改部分代码，再按运行]

运行代码框

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<script type="text/javascript">
function init(){
var staDate = new Date();
var doc = window.document;
for(var i=0;i<100;i++){
//if(container.childNodes.length>0){
//var oDiv = container.lastChild.cloneNode(true);
//oDiv.id="div_"+i;
//container.appendChild(oDiv);
//}else{
var oDiv = doc.createElement("div");
var oTab  = doc.createElement("table");
var oTbody  = doc.createElement("tbody");
var oTr = doc.createElement("tr");
var oTd = doc.createElement("td");
var oText = doc.createTextNode("毛主席向全世界宣布：中华人民共和国从此成立了");
container.appendChild(oDiv);
oDiv.appendChild(oTab);
oTab.appendChild(oTbody);
oTbody.appendChild(oTr);
oTr.appendChild(oTd);
oTd.appendChild(oText);
oDiv.id = "div_"+i;
oDiv.style.width = "400px";
oDiv.style.height = "20px";
oDiv.style.backgroundColor = "#eee";
//}
}
//alert(container.innerHTML);
alert(new Date - staDate);
}
</script>
</HEAD>
<BODY>
<div id="container"></div>
<input type="button" value="start" onclick="init();" />
</BODY>
</HTML>

[Ctrl+A 全部选择提示：你可先修改部分代码，再按运行]