How to dynamically introduce JS files

This time I will show you how to dynamically introduce JS files. What are the precautions for dynamically introducing JS files? Here are practical cases, let’s take a look.

index.html

 
  
 <meta> 
 <title> </title> 
 <script></script> 
 <script></script> 
  
  
  

test.js

alert("hello! I am test.js"); 
var str="1";

dynamic.js

//第一种方式：直接document.write 但这样会把当前的页面全覆写掉 
//document.write("<script><\/script>"); 
 
//第二种方式:动态改变已有script的src属性 
//s1.src="test.js" 
 
//第三种方式：动态创建script元素 
/* var oHead = document.getElementsByTagName(&#39;HEAD&#39;).item(0); 
 var oScript= document.createElement("script"); 
 oScript.type = "text/javascript"; 
 oScript.src="test.js"; 
 oHead.appendChild(oScript); 
*/ 
//其实原理就是利用dom动态的引入一个js到文件中来~就能和原有的js通信了~ 
//alert(str); 
 
/*以上三种方式都采用异步加载机制，也就是加载过程中，页面会往下走， 
如果这样的话会有问题的,如上面的str就访问不到，因为当程序执行alert(str)时，test.js还在加载Ing.... 
那么第四种就是基于ajax请求的,且是推荐
*/ 
function GetHttpRequest() 
{ 
 if ( window.XMLHttpRequest ) // Gecko 
 return new XMLHttpRequest() ; 
 else if ( window.ActiveXObject ) // IE 
 return new ActiveXObject("MsXml2.XmlHttp") ; 
} 
 
function ajaxPage(sId, url){ 
 var oXmlHttp = GetHttpRequest() ; 
 oXmlHttp.onreadystatechange = function() 
 { 
 if (oXmlHttp.readyState == 4) 
 { 
 includeJS( sId, url, oXmlHttp.responseText ); 
 } 
 } 
 oXmlHttp.open(&#39;GET&#39;, url, false);//同步操作 
 oXmlHttp.send(null); 
} 
 
function includeJS(sId, fileUrl, source) 
{ 
 if ( ( source != null ) && ( !document.getElementById( sId ) ) ){ 
 var oHead = document.getElementsByTagName(&#39;HEAD&#39;).item(0); 
 var oScript = document.createElement( "script" ); 
 oScript.type = "text/javascript"; 
 oScript.id = sId; 
 oScript.text = source; 
 oHead.appendChild( oScript ); 
 } 
} 
ajaxPage( "scrA", "test.js" ); 
alert( "主页面动态加载JS脚本。"); 
alert( "主页面动态加载a.js并取其中的变量：" + str );</script>

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!

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