search
HomeWeb Front-endJS TutorialHow to make dynamically inserted javascript script code run. _javascript skills

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>


<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。
Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Node.js Streams with TypeScriptNode.js Streams with TypeScriptApr 30, 2025 am 08:22 AM

Node.js excels at efficient I/O, largely thanks to streams. Streams process data incrementally, avoiding memory overload—ideal for large files, network tasks, and real-time applications. Combining streams with TypeScript's type safety creates a powe

Python vs. JavaScript: Performance and Efficiency ConsiderationsPython vs. JavaScript: Performance and Efficiency ConsiderationsApr 30, 2025 am 12:08 AM

The differences in performance and efficiency between Python and JavaScript are mainly reflected in: 1) As an interpreted language, Python runs slowly but has high development efficiency and is suitable for rapid prototype development; 2) JavaScript is limited to single thread in the browser, but multi-threading and asynchronous I/O can be used to improve performance in Node.js, and both have advantages in actual projects.

The Origins of JavaScript: Exploring Its Implementation LanguageThe Origins of JavaScript: Exploring Its Implementation LanguageApr 29, 2025 am 12:51 AM

JavaScript originated in 1995 and was created by Brandon Ike, and realized the language into C. 1.C language provides high performance and system-level programming capabilities for JavaScript. 2. JavaScript's memory management and performance optimization rely on C language. 3. The cross-platform feature of C language helps JavaScript run efficiently on different operating systems.

Behind the Scenes: What Language Powers JavaScript?Behind the Scenes: What Language Powers JavaScript?Apr 28, 2025 am 12:01 AM

JavaScript runs in browsers and Node.js environments and relies on the JavaScript engine to parse and execute code. 1) Generate abstract syntax tree (AST) in the parsing stage; 2) convert AST into bytecode or machine code in the compilation stage; 3) execute the compiled code in the execution stage.

The Future of Python and JavaScript: Trends and PredictionsThe Future of Python and JavaScript: Trends and PredictionsApr 27, 2025 am 12:21 AM

The future trends of Python and JavaScript include: 1. Python will consolidate its position in the fields of scientific computing and AI, 2. JavaScript will promote the development of web technology, 3. Cross-platform development will become a hot topic, and 4. Performance optimization will be the focus. Both will continue to expand application scenarios in their respective fields and make more breakthroughs in performance.

Python vs. JavaScript: Development Environments and ToolsPython vs. JavaScript: Development Environments and ToolsApr 26, 2025 am 12:09 AM

Both Python and JavaScript's choices in development environments are important. 1) Python's development environment includes PyCharm, JupyterNotebook and Anaconda, which are suitable for data science and rapid prototyping. 2) The development environment of JavaScript includes Node.js, VSCode and Webpack, which are suitable for front-end and back-end development. Choosing the right tools according to project needs can improve development efficiency and project success rate.

Is JavaScript Written in C? Examining the EvidenceIs JavaScript Written in C? Examining the EvidenceApr 25, 2025 am 12:15 AM

Yes, the engine core of JavaScript is written in C. 1) The C language provides efficient performance and underlying control, which is suitable for the development of JavaScript engine. 2) Taking the V8 engine as an example, its core is written in C, combining the efficiency and object-oriented characteristics of C. 3) The working principle of the JavaScript engine includes parsing, compiling and execution, and the C language plays a key role in these processes.

JavaScript's Role: Making the Web Interactive and DynamicJavaScript's Role: Making the Web Interactive and DynamicApr 24, 2025 am 12:12 AM

JavaScript is at the heart of modern websites because it enhances the interactivity and dynamicity of web pages. 1) It allows to change content without refreshing the page, 2) manipulate web pages through DOMAPI, 3) support complex interactive effects such as animation and drag-and-drop, 4) optimize performance and best practices to improve user experience.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

MantisBT

MantisBT

Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

MinGW - Minimalist GNU for Windows

MinGW - Minimalist GNU for Windows

This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

SublimeText3 English version

SublimeText3 English version

Recommended: Win version, supports code prompts!

PhpStorm Mac version

PhpStorm Mac version

The latest (2018.2.1) professional PHP integrated development tool

EditPlus Chinese cracked version

EditPlus Chinese cracked version

Small size, syntax highlighting, does not support code prompt function