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。
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:
- 防止js加载阻塞页面渲染
- 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>
基本API
require会定义三个变量:define,require,requirejs,其中require === requirejs,一般使用require更简短
- define 从名字就可以看出这个api是用来定义一个模块
- require 加载依赖模块,并执行加载完后的回调函数
前一篇中的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>
通过define函数定义了一个模块,然后再页面中使用:
<span class="kwd">require</span><span class="pun">([</span><span class="str">"js/a"</span><span class="pun">]);</span>
来加载该模块(注意require中的依赖是一个数组,即使只有一个依赖,你也必须使用数组来定义),requir API的第二个参数是callback,一个function,是用来处理加载完毕后的逻辑,如:
<span class="kwd">require</span><span class="pun">([</span><span class="str">"js/a"</span><span class="pun">],</span><span class="kwd">function</span><span class="pun">(){</span><span class="pln"> alert</span><span class="pun">(</span><span class="str">"load finished"</span><span class="pun">);</span><span class="pln"> </span><span class="pun">})</span>
加载文件
之前的例子中加载模块都是本地js,但是大部分情况下网页需要加载的JS可能来自本地服务器、其他网站或CDN,这样就不能通过这种方式来加载了,我们以加载一个jquery库为例:
<span class="kwd">require</span><span class="pun">.</span><span class="pln">config</span><span class="pun">({</span><span class="pln"> paths </span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="str">"jquery"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="pun">[</span><span class="str">"http://libs.baidu.com/jquery/2.0.3/jquery"</span><span class="pun">]</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">})</span><span class="pln"> </span><span class="kwd">require</span><span class="pun">([</span><span class="str">"jquery"</span><span class="pun">,</span><span class="str">"js/a"</span><span class="pun">],</span><span class="kwd">function</span><span class="pun">(</span><span class="pln">$</span><span class="pun">){</span><span class="pln"> $</span><span class="pun">(</span><span class="kwd">function</span><span class="pun">(){</span><span class="pln"> alert</span><span class="pun">(</span><span class="str">"load finished"</span><span class="pun">);</span><span class="pln"> </span><span class="pun">})</span><span class="pln"> </span><span class="pun">})</span>
这边涉及了require.config
,require.config
是用来配置模块加载位置,简单点说就是给模块起一个更短更好记的名字,比如将百度的jquery库地址标记为jquery
,这样在require时只需要写["jquery"]
就可以加载该js,本地的js我们也可以这样配置:
<span class="kwd">require</span><span class="pun">.</span><span class="pln">config</span><span class="pun">({</span><span class="pln"> paths </span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="str">"jquery"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="pun">[</span><span class="str">"http://libs.baidu.com/jquery/2.0.3/jquery"</span><span class="pun">],</span><span class="pln"> </span><span class="str">"a"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="str">"js/a"</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">})</span><span class="pln"> </span><span class="kwd">require</span><span class="pun">([</span><span class="str">"jquery"</span><span class="pun">,</span><span class="str">"a"</span><span class="pun">],</span><span class="kwd">function</span><span class="pun">(</span><span class="pln">$</span><span class="pun">){</span><span class="pln"> $</span><span class="pun">(</span><span class="kwd">function</span><span class="pun">(){</span><span class="pln"> alert</span><span class="pun">(</span><span class="str">"load finished"</span><span class="pun">);</span><span class="pln"> </span><span class="pun">})</span><span class="pln"> </span><span class="pun">})</span>
通过paths的配置会使我们的模块名字更精炼,paths还有一个重要的功能,就是可以配置多个路径,如果远程cdn库没有加载成功,可以加载本地的库,如:
<span class="kwd">require</span><span class="pun">.</span><span class="pln">config</span><span class="pun">({</span><span class="pln"> paths </span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="str">"jquery"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="pun">[</span><span class="str">"http://libs.baidu.com/jquery/2.0.3/jquery"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"js/jquery"</span><span class="pun">],</span><span class="pln"> </span><span class="str">"a"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="str">"js/a"</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">})</span><span class="pln"> </span><span class="kwd">require</span><span class="pun">([</span><span class="str">"jquery"</span><span class="pun">,</span><span class="str">"a"</span><span class="pun">],</span><span class="kwd">function</span><span class="pun">(</span><span class="pln">$</span><span class="pun">){</span><span class="pln"> $</span><span class="pun">(</span><span class="kwd">function</span><span class="pun">(){</span><span class="pln"> alert</span><span class="pun">(</span><span class="str">"load finished"</span><span class="pun">);</span><span class="pln"> </span><span class="pun">})</span><span class="pln"> </span><span class="pun">})</span>
这样配置后,当百度的jquery没有加载成功后,会加载本地js目录下的jquery
-
在使用requirejs时,加载模块时不用写
.js
后缀的,当然也是不能写后缀 -
上面例子中的callback函数中发现有
$
参数,这个就是依赖的jquery
模块的输出变量,如果你依赖多个模块,可以依次写入多个参数来使用:
<span class="kwd">require</span><span class="pun">([</span><span class="str">"jquery"</span><span class="pun">,</span><span class="str">"underscore"</span><span class="pun">],</span><span class="kwd">function</span><span class="pun">(</span><span class="pln">$</span><span class="pun">,</span><span class="pln"> _</span><span class="pun">){</span><span class="pln"> $</span><span class="pun">(</span><span class="kwd">function</span><span class="pun">(){</span><span class="pln"> _</span><span class="pun">.</span><span class="pln">each</span><span class="pun">([</span><span class="lit">1</span><span class="pun">,</span><span class="lit">2</span><span class="pun">,</span><span class="lit">3</span><span class="pun">],</span><span class="pln">alert</span><span class="pun">);</span><span class="pln"> </span><span class="pun">})</span><span class="pln"> </span><span class="pun">})</span>
如果某个模块不输出变量值,则没有,所以尽量将输出的模块写在前面,防止位置错乱引发误解
全局配置
上面的例子中重复出现了require.config
配置,如果每个页面中都加入配置,必然显得十分不雅,requirejs提供了一种叫”主数据”的功能,我们首先创建一个main.js:
<span class="kwd">require</span><span class="pun">.</span><span class="pln">config</span><span class="pun">({</span><span class="pln"> paths </span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="str">"jquery"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="pun">[</span><span class="str">"http://libs.baidu.com/jquery/2.0.3/jquery"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"js/jquery"</span><span class="pun">],</span><span class="pln"> </span><span class="str">"a"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="str">"js/a"</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">})</span>
然后再页面中使用下面的方式来使用requirejs:
<span class="tag"><script</span><span class="pln"> </span><span class="atn">data-main</span><span class="pun">=</span><span class="atv">"js/main"</span><span class="pln"> </span><span class="atn">src</span><span class="pun">=</span><span class="atv">"js/require.js"</span><span class="tag">></script></span>
解释一下,加载requirejs脚本的script标签加入了data-main
属性,这个属性指定的js将在加载完reuqire.js后处理,我们把require.config
的配置加入到data-main
后,就可以使每一个页面都使用这个配置,然后页面中就可以直接使用require
来加载所有的短模块名
data-main
还有一个重要的功能,当script标签指定data-main属性时,require会默认的将data-main指定的js为根路径,是什么意思呢?如上面的data-main="js/main"
设定后,我们在使用require([’jquery’])
后(不配置jquery的paths),require会自动加载js/jquery.js这个文件,而不是jquery.js,相当于默认配置了:
<span class="kwd">require</span><span class="pun">.</span><span class="pln">config</span><span class="pun">({</span><span class="pln"> baseUrl </span><span class="pun">:</span><span class="pln"> </span><span class="str">"js"</span><span class="pln"> </span><span class="pun">})</span>
第三方模块
通过require
加载的模块一般都需要符合AMD规范即使用define
来申明模块,但是部分时候需要加载非AMD规范的js,这时候就需要用到另一个功能:shim,shim解释起来也比较难理解,shim直接翻译为”垫”,其实也是有这层意思的,目前我主要用在两个地方
1.
非AMD模块输出,将非标准的AMD模块”垫”成可用的模块,例如:在老版本的jquery中,是没有继承AMD规范的,所以不能直接
require[“jquery”],这时候就需要shim,比如我要是用underscore类库,但是他并没有实现AMD规范,那我们可以这样配置
<span class="kwd">require</span><span class="pun">.</span><span class="pln">config</span><span class="pun">({</span><span class="pln"> shim</span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="str">"underscore"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> exports </span><span class="pun">:</span><span class="pln"> </span><span class="str">"_"</span><span class="pun">;</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">})</span>
这样配置后,我们就可以在其他模块中引用underscore模块:
<span class="kwd">require</span><span class="pun">([</span><span class="str">"underscore"</span><span class="pun">],</span><span class="pln"> </span><span class="kwd">function</span><span class="pun">(</span><span class="pln">_</span><span class="pun">){</span><span class="pln"> _</span><span class="pun">.</span><span class="pln">each</span><span class="pun">([</span><span class="lit">1</span><span class="pun">,</span><span class="lit">2</span><span class="pun">,</span><span class="lit">3</span><span class="pun">],</span><span class="pln"> alert</span><span class="pun">);</span><span class="pln"> </span><span class="pun">})</span>
- 插件形式的非AMD模块,我们经常会用到jquery插件,而且这些插件基本都不符合AMD规范,比如jquery.form插件,这时候就需要将form插件”垫”到jquery中:
<span class="kwd">require</span><span class="pun">.</span><span class="pln">config</span><span class="pun">({</span><span class="pln"> shim</span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="str">"underscore"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> exports </span><span class="pun">:</span><span class="pln"> </span><span class="str">"_"</span><span class="pun">;</span><span class="pln"> </span><span class="pun">},</span><span class="pln"> </span><span class="str">"jquery.form"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> deps </span><span class="pun">:</span><span class="pln"> </span><span class="pun">[</span><span class="str">"jquery"</span><span class="pun">]</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">})</span>
也可以简写为:
<span class="kwd">require</span><span class="pun">.</span><span class="pln">config</span><span class="pun">({</span><span class="pln"> shim</span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="str">"underscore"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> exports </span><span class="pun">:</span><span class="pln"> </span><span class="str">"_"</span><span class="pun">;</span><span class="pln"> </span><span class="pun">},</span><span class="pln"> </span><span class="str">"jquery.form"</span><span class="pln"> </span><span class="pun">:</span><span class="pln"> </span><span class="pun">[</span><span class="str">"jquery"</span><span class="pun">]</span><span class="pln"> </span><span class="pun">}</span><span class="pln"> </span><span class="pun">})</span>
这样配置之后我们就可以使用加载插件后的jquery了
<span class="kwd">require</span><span class="pun">.</span><span class="pln">config</span><span class="pun">([</span><span class="str">"jquery"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"jquery.form"</span><span class="pun">],</span><span class="pln"> </span><span class="kwd">function</span><span class="pun">(</span><span class="pln">$</span><span class="pun">){</span><span class="pln"> $</span><span class="pun">(</span><span class="kwd">function</span><span class="pun">(){</span><span class="pln"> $</span><span class="pun">(</span><span class="str">"#form"</span><span class="pun">).</span><span class="pln">ajaxSubmit</span><span class="pun">({...});</span><span class="pln"> </span><span class="pun">})</span><span class="pln"> </span><span class="pun">})</span>
好了,requirejs的基本配置大致就是这么多,还有一些扩展的功能会在之后的篇幅中提到
文章来源:https://github.com/liuxey/blog/issues/1