随着网站功能逐渐丰富,网页中的js也变得越来越复杂和臃肿,原有通过script标签来导入一个个的js文件这种方式已经不能满足现在互联网开发模式,我们需要团队协作、模块复用、单元测试等等一系列复杂的需求。

【思维导图】JS模块化工具requirejs教程:初识requirejs

RequireJS是一个非常小巧的JavaScript模块载入框架,是AMD规范最好的实现者之一。最新版本的RequireJS压缩后只有14K,堪称非常轻量。它还同时可以和其他的框架协同工作,使用RequireJS必将使您的前端代码质量得以提升。

requirejs能带来什么好处

官方对requirejs的描述:

RequireJS is a JavaScript file and module loader. It is optimized
for in-browser use, but it can be used in other JavaScript environments,
like Rhino and Node. Using a modular script loader like RequireJS will
improve the speed and quality of your code.

大致意思:

在浏览器中可以作为js文件的模块加载器,也可以用在Node和Rhino环境,balabala…。这段话描述了requirejs的基本功能”模块化加载”,什么是模块化加载?我们要从之后的篇幅中一一解释

先来看一段常见的场景,通过示例讲解如何运用requirejs

正常编写方式

index.html:

<span class="dec"><!DOCTYPE html></span><span class="pln"> </span><span class="tag"><html></span><span class="pln"> </span><span class="tag"><head></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"a.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"></head></span><span class="pln"> </span><span class="tag"><body></span><span class="pln"> </span><span class="tag"><span></span><span class="pln">body</span><span class="tag"></span></span><span class="pln"> </span><span class="tag"></body></span><span class="pln"> </span><span class="tag"></html></span>

a.js:

<span class="kwd">function</span><span class="pln"> fun1</span><span class="pun">(){</span><span class="pln"> alert</span><span class="pun">(</span><span class="str">"it works"</span><span class="pun">);</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> fun1</span><span class="pun">();</span>

可能你更喜欢这样写

<span class="pun">(</span><span class="kwd">function</span><span class="pun">(){</span><span class="pln"> </span><span class="kwd">function</span><span class="pln"> fun1</span><span class="pun">(){</span><span class="pln"> alert</span><span class="pun">(</span><span class="str">"it works"</span><span class="pun">);</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> fun1</span><span class="pun">();</span><span class="pln"> </span><span class="pun">})()</span>

第二种方法使用了块作用域来申明function防止污染全局变量,本质还是一样的,当运行上面两种例子时不知道你是否注意到,alert执行的时候,html内容是一片空白的,即<span>body</span>并未被显示,当点击确定后,才出现,这就是JS阻塞浏览器渲染导致的结果。

requirejs写法

当然首先要到requirejs的网站去下载js -> requirejs.rog
index.html:

<span class="dec"><!DOCTYPE html></span><span class="pln"> </span><span class="tag"><html></span><span class="pln"> </span><span class="tag"><head></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"require.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="tag">></span><span class="pln"> require</span><span class="pun">([</span><span class="str">"a"</span><span class="pun">]);</span><span class="pln"> </span><span class="tag"></script></span><span class="pln"> </span><span class="tag"></head></span><span class="pln"> </span><span class="tag"><body></span><span class="pln"> </span><span class="tag"><span></span><span class="pln">body</span><span class="tag"></span></span><span class="pln"> </span><span class="tag"></body></span><span class="pln"> </span><span class="tag"></html></span>

a.js:

<span class="pln">define</span><span class="pun">(</span><span class="kwd">function</span><span class="pun">(){</span><span class="pln"> </span><span class="kwd">function</span><span class="pln"> fun1</span><span class="pun">(){</span><span class="pln"> alert</span><span class="pun">(</span><span class="str">"it works"</span><span class="pun">);</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> fun1</span><span class="pun">();</span><span class="pln"> </span><span class="pun">})</span>

浏览器提示了”it works”,说明运行正确,但是有一点不一样,这次浏览器并不是一片空白,body已经出现在页面中,目前为止可以知道requirejs具有如下优点:

  1. 防止js加载阻塞页面渲染
  2. 使用程序调用的方式加载js,防出现如下丑陋的场景
<span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"a.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"b.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"c.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"d.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"e.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"f.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"g.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"h.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"i.js"</span><span class="tag">></script></span><span class="pln"> </span><span class="tag"><script</span><span class="pln"> </span><span class="atn">type</span><span class="pun">=</span><span class="atv">"text/javascript"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"j.js"</span><span class="tag">></script></span>