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Detailed explanation of how JavaScript uses advanced modular require.js

黄舟

Nov 01, 2017 am 09:58 AM

javascript

This article introduces the specific use of require.js, share it with everyone, and leave a note for yourself.

Require.js:

RequireJS is a very small javascript module loading framework, which is AMD (Asynchronous Module Definition, One of the best implementations of the asynchronous module loading mechanism) specification. The latest version of requireJS is only 14k compressed, which is very lightweight. It can also work in coordination with other frameworks. Using requireJS will definitely improve the quality of our front-end code.

First of all, let’s take a look at a normal page js loading

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title></title>
    <script type="text/javascript" src="js/index02.js" ></script>
  </head>
  <body>
    <h1>this is a page.</h1>
  </body>
</html>

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Running results:

At this time, if we don’t pop up correctly If the box is operated, the page will not load and there will be no page content. This is not the result we want to achieve.

Below we use require.js to operate:

index.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title></title>
    <script src="js/require2.1.11.js"></script>
    <script type="text/javascript">
      require(["js/index","js/index01"],function(){
        console.log("当js加载成功后会执行的函数");
      },function(){
        console.log("当js加载失败后会执行的函数");
      });
    </script>
  </head>
  <body>
  </body>
</html>

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index.js

define(function(){
  console.log("this is a test!");
  function test(){
    console.log("haha,i am a test!");
  }
  test();
});

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First of all, test02.js is no longer imported on the page , only requireJS is imported. Secondly, in JavaScript, we use the require() method, passing an array of parameters. The actual parameter is the [path + file name of the js file we want to import.

The running result at this time:

You can see it out, the content of the page has been displayed. Instead of waiting for the page to load after the js is completed, as we did before, the js code is run only after the page is loaded, which greatly improves the operating efficiency.

According to the above code, we can analyze the basic API of requirejs:

requireJS will define three variables: define, require, requirejs

require==requirejs, generally using require is shorter.
define is used to define a module
require to load dependent modules (references defined modules) and execute The callback function after loading

##require has three parameters:

require(["js/index","js/index01"],function(){
        console.log("当js加载成功后会执行的函数");
      },function(){
        console.log("当js加载失败后会执行的函数");
      });
//第一个参数：定义require中的依赖，参数必须是数组形式，即使只有一个依赖，也必须使用数组形式传参。
//第二个参数：是一个回调函数，用来处理加载完毕后的逻辑，当所有模块加载完成后触发
//第三个参数：也是一个回调函数，用来处理模块加载失败后的情况。如上面代码，js中没有定义index01.js这个文件，所以出调用这个回调函数。

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Load network file

Before, we loaded local js files, but sometimes we need to load files on the network, so how to load them? Now let's introduce how to load js files on the Internet.

Let's take loading a

jquery.js file as an example:

//百度cdn公共库jQuery地址：   http://apps.bdimg.com/libs/jquery/2.1.1/jquery.js 
//jQuery官方地址：      https://code.jquery.com/jquery-3.1.1.js
//注意：网络上去取时不能加后缀，否则取不到
require.config({
  paths : {
    //为网络上的库去一个名字：jquery
    "jquery" : ["https://code.jquery.com/jquery-3.1.1"]
  }
});

//
require(["jquery","js/test01","js/test02"],function(){
  alert("页面加载成功~~");
},function(){
  alert("页面加载失败~~")
});

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Fetching js files on the Internet Note when writing the file:

1. The parameter of the config method is an object.

2. The value of paths is also an object.
3. When we choose a name for the library on the network, it is arbitrary, but it is recommended to A meaningful name, others can know what your network resources are through the name
4. The value of the library is an array, which means multiple writes can be written at the same time to prevent network abnormalities from being accessed
5. Pay special attention : The network resource path cannot have a suffix name, otherwise it will not be obtained
6. We can also get it from the network first. If it cannot be obtained, then obtain it locally to reduce the pressure on local services (it belongs to project optimization).

require.config({
  paths : {
    //这样配置，减轻本地服务器的压力
    "jquery" : ["https://code.jquery.com/jquery-3.1.1.js","js/jquery-1.8.3"]
  }
});

//
require(["jquery","js/test01","js/test02"],function(){
  alert("页面加载成功~~");
},function(){
  alert("页面加载失败~~")
});

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Similarly, we can also add local configuration to paths:

require.config({
  paths : {
    //这样配置，减轻本地服务器的压力
    "jquery" : ["https://code.jquery.com/jquery-3.1.1","js/jquery-1.8.3"],
    //将本地的js文件同样配置，之后引用
    "test01" : ["js/test01"],
    "test02" : ["js/test02"]
  }
});

//
require(["jquery","test01","test02"],function(){
  alert("页面加载成功~~");
},function(){
  alert("页面加载失败~~")
});

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The require.config configuration appears repeatedly in the above example. If the configuration is added to each page, it will definitely look very special. No, requirejs provides a function called "master data". We first create a main.js:

require.config({
  paths : {
    //这样配置，减轻本地服务器的压力
    "jquery" : ["https://code.jquery.com/jquery-3.1.1","js/jquery-1.8.3"],
    //将本地的js文件同样配置，之后引用
    "test01" : ["js/test01"],
    "test02" : ["js/test02"]
  }
});

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and then use requirejs in the following way on the page:

<script type="text/javascript" src="js/require2.1.11.js" ></script>
<script type="text/javascript" src="js/main.js" ></script>
<script type="text/javascript">

  require(["jquery","t1","t2"],function(){
    alert("页面加载成功~~");
  },function(){
    alert("页面加载失败~~")
  });

</script>

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The official provides a method based on tag attributes:

<script data-main="js/main" src="js/require2.1.11.js" ></script>

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Place all configurations and imported js in main.js, so that only such a tag is needed on the page.

The code demonstration is as follows:

//test01.js--定义一个js模块
define(function(){
  function test(){
    console.log("this is test01.js");
  }
  test();

  $("p").css("color","#DB7093");
});

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//main.js--requirejs的全局配置
require.config({
  paths:{
    "jquery":["jquery-1.8.3"],
    "test":["test01"]
  },
  shim:{
    "test":["jquery"]
  }
});
require(["test"],function(){
  console.log("success!");
});

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//index.html--此时，引入js文件只需一行代码
<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title></title>
    <script type="text/javascript" data-main = "js/main" src="js/require2.1.11.js" ></script>
  </head>
  <body>
    <p>i am liyanan and this is a testn Page.</p>
  </body>
</html>

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