Home Web Front-end JS Tutorial How to make dynamically inserted javascript script code run. _javascript skills

How to make dynamically inserted javascript script code run. _javascript skills

May 16, 2016 pm 07:21 PM

首先,声明方法很多种,直接间接的方法都有,只罗列一般情况下的两种模式:
假设我们要装入的代码是a.js:
var foo=function(){
document.write("I am a.js content foo() function by never-online");
};

一。直接插入src,这种方法简单而直接,但有局限性,
1)
<script> <BR>var x=document.createElement("SCRIPT"); <BR>x.src="a.js"; x.defer=true; <BR>document.getElementsByTagName("HEAD")[0].appendChild(x); <BR>foo(); <BR></script>


在如上的代码放上head标签内,执行时大多数情况下是会出错,信息为:错误:缺少对象
这是由于动态创建对象script时,则于a.js还没有完全载入而导致的。执行下面的代码,你就可以发现原因了。



never-online dynamic code test page


 <br><br>readyState的含义 <br> - uninitialized : 脚本对象刚被创建,脚本代码未载入; <br> - loading : 脚本代码载入中; <br> - loaded : 脚本代码完成读入,但尚未开始解释执行; <br> - interactive : 解释执行过程中; <br> - complete : 脚本已经执行完成。 <br><br>
Copy after login


<script> <br><br>window.onerror=function(msg,url,line){ <BR> document.getElementById("viewer").innerHTML+='<p style="color:red">错误:'+msg+'line:'+line+''; <BR> return true; <BR>} <br><br>function bar(u) { <BR> var x=document.createElement("SCRIPT"); <BR> x.src=u; <BR> x.defer=true; <BR> document.getElementsByTagName("HEAD")[0].appendChild(x); <BR>} <BR>bar("a.js"); <br><br>(function getReadyState(){ <BR> var e=document.getElementById("viewer") <BR> var x=true; <BR> var a = document.getElementsByTagName("SCRIPT"); <BR> for (var i=0; i<a.length; i++) { <BR> if (a[i].readyState=='complete' && x!=false) x=true; else x=false <BR> e.innerHTML+=(a[i].src?a[i].src+':':'noname:')+a[i].readyState+"<br />"; <BR> } <BR> e.innerHTML+="<hr/>"; <BR> if (x) window.clearTimeout(window.timer); else <BR> window.timer=window.setTimeout('getReadyState()',1000); <BR>}()); <br><br>foo(); <br><br></script>
<script> <BR>//<![CDATA[ <BR>foo(); <BR>//]]> <BR></script>


初始值为:
a.js:loading
noname:interactive
我们可以知道,a.js依然在loading状态,在执行foo()当然是错误的。但下一个script标签执行中,a.js的readyState是complete了,所以可以执行foo()的函数。由此,我推荐你可以简单的这样运用动态用生成script标签方法来添加js的url。
解决方法如下
1)用window.setTimeout方法来执行,估计a.js已经载入完毕,才执行a.js里的函数。这个方法仍然不保险
<script> <BR>var x=document.createElement("SCRIPT"); <BR>x.src="a.js"; x.defer=true; <BR>document.getElementsByTagName("HEAD")[0].appendChild(x); <BR>window.setTimeout('foo()',1000); <BR></script>
2)多加一个script标签放置要执行的代码
<script> <BR>var x=document.createElement("SCRIPT"); <BR>x.src="a.js"; x.defer=true; <BR>document.getElementsByTagName("HEAD")[0].appendChild(x); <BR></script>
<script> <BR>//多一个script标签来放置 <BR>//这里a.js的readyState已经为complete了。 <BR>foo(); <BR></script>

二、用XMLHttpRequest和window.execScript动态的执行a.js,这个方法的优点比较明显,但效率可能有所下降,没有测试,有兴趣的朋友可以自己测试一下速度。
代码如下:
<script> <BR>function bar(u) { <BR> var x=window.ActiveXObject?new ActiveXObject("MSXML2.XMLHTTP"):new XMLHttpRequest(); <BR> x.open("GET",u,false); <BR> x.send(null); <BR> s=x.responseText; <BR> try {window.execScript(s)}catch(ex){window.eval(s)};//Mozilla下window.eval大致与IE的window.execScript方法功能相同 <BR>} <BR>bar("a.js"); <BR>foo(); <BR></script>
但这个方法仍有缺点,也就是a.js脚本中的代码有中文的情况,如何处理?那就要经常解码了,而解码恰恰是js的软肋,如果运用vbs来解码,那么兼容也就没有了。要看自己具体的应用了,我在neverModules里加载js包时用的就是window.execScript方法来解析代码,这样更可以配合js namespace的应用

顺便再加上解码

 <script> <BR> //<![CDATA[ <BR> function bar(u) { <BR> var x=window.ActiveXObject?new ActiveXObject("MSXML2.XMLHTTP"):new XMLHttpRequest(); <BR> x.open("GET",u,false); <BR> x.send(null); <BR> s=parseScript(x.responseText); <BR> try {window.execScript(s)}catch(ex){window.eval(s)}; <BR> } <BR> function parseScript(jscode) { <BR> // --- toCurrentCharset(), by aimingoo 解码 <BR> window.execScript(''+ <BR> 'Function Asc2Unicode(n) \n'+ <BR> ' Asc2Unicode = Chr(n) \n'+ <BR> 'End Function \n'+ <br><br> 'Function SafeArray2Str(body) \n'+ <BR> ' SafeArray2Str = CStr(body)\n'+ <BR> 'End Function','VBScript'); <br><br> var r1 = /%u(..)(..)/g, r2 = /%([8,9,A-F].)%(..)/g; <BR> var toUnicode = function($0, $1, $2) {return Asc2Unicode(parseInt($1+$2, 16))} <BR> toCurrentCharset = function(body) { <BR> return unescape(escape(SafeArray2Str(body)).replace(r1, "%$2%$1").replace(r2, toUnicode)); <BR> }; jscode=toCurrentCharset(jscode); <BR> window.execScript(jscode, 'JavaScript'); //IE有效,vbs解码 <BR> return jscode; <BR> } <br><br> bar('a.js'); <br><br> foo(); <BR> //]]> <BR> </script>

不过大多数的情况下,第二种方法处理起来应该没有问题,如果要很严格的执行的话,第一种方法还是有改进的代码的,比如加载a.js的内容,把本身的脚本再次解析再执行,但复杂度就提高了,所以要有一个非常完美的解决方案,还需要更进一步来讨论。
我就不写这么多了,仅仅为一个提醒,还有一个抛砖引玉的作用。
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