Detailed explanation of the difference between exports and module.exports in seaJs

This article mainly introduces the difference between exports and module.exports based on the experience of using seaJs. It analyzes the specific functions, usage methods and related operation precautions of exports and module.exports in the form of examples. Friends in need can refer to it

The example in this article describes the difference between exports and module.exports based on the experience of using seaJs. Share it with everyone for your reference, the details are as follows:

1. exports is the auxiliary object of module.exports. When exports provides api to the outside world, you need to use return to return the exports object

2. module.exports also API

reference can be provided directly to the outside world: https://github.com/seajs/seajs/issues/242

exports Object

exports is an object used to provide module interfaces to the outside world.

define(function(require, exports) {
 // 对外提供 foo 属性
 exports.foo = 'bar';
 // 对外提供 doSomething 方法
 exports.doSomething = function() {};
});

In addition to adding members to the exports object, you can also use return to directly provide interfaces to the outside world.

define(function(require) {
 // 通过 return 直接提供接口
 return {
  foo: 'bar',
  doSomething: function() {}
 };
});

If the return statement is the only code in the module, it can also be simplified to:

define({
 foo: 'bar',
 doSomething: function() {}
});

The above The format is particularly suitable for defining JSONP modules.

Special note: The following way of writing is wrong!

define(function(require, exports) {
 // 错误用法！！!
 exports = {
  foo: 'bar',
  doSomething: function() {}
 };
});

The correct way to write it is to use return or assign a value to module.exports:

define(function(require, exports, module) {
 // 正确写法
 module.exports = {
  foo: 'bar',
  doSomething: function() {}
 };
});

Tips: exports is just a reference to module.exports. When exports is reassigned inside the factory, the value of module.exports will not be changed. Therefore, assigning a value to exports is invalid and cannot be used to change the module interface.

module.exports Object

The interface provided by the current module.

The exports parameter passed to the factory constructor is a reference to the module.exports object. Providing interfaces only through the exports parameter sometimes cannot meet all the needs of developers. For example, when the interface of a module is an instance of a certain class, it needs to be implemented through module.exports:

define(function(require, exports, module) {
 // exports 是 module.exports 的一个引用
 console.log(module.exports === exports); // true
 // 重新给 module.exports 赋值
 module.exports = new SomeClass();
 // exports 不再等于 module.exports
 console.log(module.exports === exports); // false
});

Note: The assignment to module.exports needs to be synchronized Execution cannot be placed in the callback function. The following does not work:

// x.jsdefine(function(require, exports, module) {
 // 错误用法
 setTimeout(function() {
  module.exports = { a: "hello" };
 }, 0);
});

The above x.js is called in y.js:

// y.jsdefine(function(require, exports, module) {
 var x = require('./x');
 // 无法立刻得到模块 x 的属性 a
 console.log(x.a); // undefined
});

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