Detailed explanation of JavaScript modular programming

This article explains JavaScript modular programming in detail

Chapter 1 JavaScript modular programming

(1): How to write modules

-Original writing method
/ / A module is a set of methods to implement a specific function; as long as different functions (and variables that record status) are simply put together, it is considered a module;
function m1(){
                                                                                                                                                                                                                    m1(){ ), form a module; just call it directly when using;
// Disadvantages: "pollution" of global variables; there is no guarantee that variable names will not conflict with other modules, and there is no direct relationship between module members;

二
Object
How to write

// 把模块写成一个对象,所有的模块成员都放到这个对象里面;
  var module = new Object({
    _count:0,
    m1:function(){
      // ...
    },
    m2:function(){
      // ...
    }
  });
// 上面的函数m1()和m2(),都封装在module对象里;使用时直接调用这个对象的属性;
  module.m1();
// 但是,这样的写法会暴露所有模块成员,内部状态可以被外部改写;
  module._count = 4;

Three how to write the immediate execution function

  var module = (function(){
    var _count = 0;
    var m1 = function(){
      // ...
    };
    var m2 = function(){

    };
    return {
      m1:m1,
      m2:m2
    };
  })();
// 使用上面的写法,外部代码无法读取内部的_count变量;
  console.info(module._count); // undefined;
// 上面的写法就是JavaScript模块的基本写法;

Four-wide zoom mode

// 如果模块很大,必须分成几个部分,或者一个模块需要继承另一个模块,这时就有必要采用"放大模式";
  var module = (function(mod){
    mod.m3 = function(){
      // ...
    };
    return mod;
  })(module);
// 上面的代码为module模块添加了一个新方法m3(),然后返回新的module模块;

Five-wide zoom mode

// 在浏览器环境中,模块的各个部分通常都是从网上获取的,有时无法知道哪个部分会先加载;
// 如果采用上一节的写法,第一个执行的部分有可能加载一个不存在的空对象,这时就要采用"宽放大模式";
  var module = (function(mod){
    // ...
    return mod;
  })(window.module || {});
// 与"放大模式"相比,"宽放大模式"就是"立即执行函数"的参数可以是空对象;

Six input global variables

// 独立性是模块的重要特点,模块内部最好不与程序的其他部分直接交互;
// 为了在模块内部调用全局变量,必须显式地将其他变量输入模块;
  var module = (function($,YAHOO){
    // ...
  })(jQuery,YAHOO);
// 上面的module模块需要使用jQuery库和YUI库,就把这两个库(其实是两个模块)当作参数输入module;
// 这样做除了保证模块的独立性,还使得模块之间的依赖关系变得明显;

Chapter 2 JavaScript Modular Programming (2): AMD Specification

One Module Specification
// Currently, there are two popular JavaScript module specifications: CommonJS and AMD;

二CommonJS

node.js
Using javascript language for server-side programming marks the official birth of "JavaScript modular programming";

In CommonJS, there is a global method
require(), which is used to load modules; var math = require('math'); // Load module;
math.add(2,3); //Call module method=>5;
Three browser environment//The code in the previous section runs in the browser There will be a big problem;
var math = require('math');
math.add(2,3);

// Therefore, the browser module cannot use "synchronous loading" and can only use "asynchronous loading";==>AMD;

四AMD
AMD (Asyn
chr
onous Module Definition) asynchronous module definition;

callback function
, // This callback function will not run until the loading is completed; // AMD also uses the require() statement to load the module , but it requires two parameters:
require([module],callback);// module: is an array
, the members inside are the modules to be loaded;
/ / callback: is the callback function after successful loading;
require(['math'],function(math){
math.add(2,3); });// Math.add() and math module loading are not synchronized, and the browser will not freeze; therefore, AMD is more suitable for the browser environment;

Chapter 3 JavaScript Modular Programming (3): require.js Usage
1 Why use require.js
// Multiple js files need to be loaded in sequence;
// Disadvantages:

// 2. Since there are dependencies between js files, the loading order must be strictly guaranteed. When the dependencies are complex, the writing and maintenance of the code will becomes difficult;
// So require.js solves these two problems:
// 1. Implement asynchronous loading of js files to avoid web pages losing response;
// 2. Management between modules Dependencies facilitate code writing and maintenance;

Loading of require.js
1. Loading require.js

// The async attribute indicates that this file needs to be loaded asynchronously to prevent the web page from losing response; IE does not support this attribute and only supports defer, so write defer as well;

main
.js

// data-main The function of the attribute is to specify the main module of the web program => main.js. This file will be loaded by require.js first;
// Since the default file suffix of require.js is js, you can main.js is abbreviated as main;

How to write the three main modules main.js
1. If main.js does not depend on any other modules, you can directly write JavaScript code;
// main.js
alert('Loading successful! ');
2. If main.js depends on the module, then you need to use the require() function defined by the AMD specification;
// main.js
require(['moduleA','moduleB ','moduleC'],function(moduleA,moduleB,moduleC){
// ...
})
// The require() function receives two parameters:
// Parameters One: Array, indicating the dependent modules, that is, the three modules that the main module depends on;
// Parameter two: Callback function, it will be called when all the previously specified modules are loaded successfully; the loaded module will Pass this function in as a parameter, so that these modules can be used inside the callback function;
// require() loads modules asynchronously, and the browser will not lose response; for the callback function it specifies, only the previous modules are loaded successfully It will run only after , which solves the dependency problem;
Example:
require(['jquery','underscore','backbone'],function($,_,Backbone){
/ / ...
});

The above is the detailed content of Detailed explanation of JavaScript modular programming. For more information, please follow other related articles on the PHP Chinese website!