Detailed explanation of the use of exports and module.exports of node.js and ES6-JS Tutorial-php.cn

Detailed explanation of the use of exports and module.exports of node.js and ES6

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Release： 2018-04-16 15:36:40

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This time I will bring you a detailed explanation of the use of node.js and ES6 exports and module.exports. What are the precautions when using node.js and ES6 exports and module.exports? , the following is a practical case, let’s take a look.

Ah Xi, my head is so big....

Now that we’re done, let’s sit down and sort out their scope of use.

require: Import supported by both node and es6
export / import : Only export supported by es6
module.exports / exports: Only exports supported by node

From this moment on, I felt it was time to clarify the relationship between them, otherwise I would die of confusion. Not much to say, let’s get started! !

node module

The module system in Node follows the CommonJS specification.

Then the question comes again, what is the CommonJS specification?

Because js was relatively confusing in the past, everyone wrote their own code, and there was no concept of a module, and this specification is actually a definition of a module.

The modules defined by CommonJS are divided into: module identification (module), module definition (exports), module reference (require)

First explain exports and module.exports

When a node executes a file, an exports and module object ,

will be generated in the file. And module has an exports attribute. The relationship between them is as shown below, they all point to a {} memory area.

1	`exports = module.exports = {};`

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So let’s take a look at the code.

//utils.js
let a = 100;
console.log(module.exports); //能打印出结果为：{}
console.log(exports); //能打印出结果为：{}
exports.a = 200; //这里辛苦劳作帮 module.exports 的内容给改成 {a : 200}
exports = '指向其他内存区'; //这里把exports的指向指走
//test.js
var a = require('/utils');
console.log(a) // 打印为 {a : 200}

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As can be seen from the above, in fact, the content exported by require is the content of the memory block pointed to by module.exports, not exports.

In short, the difference between them is that exports is just a reference to module.exports, which is used to assist the latter in adding content.

To put it in plain language, exports only assists module.exports in operating the data in the memory. After all the hard work of operating the data, I am exhausted. In the end, the content that is actually required is still module.exports. It is really hard work. .

In fact, if you use the concept of memory block to understand it, it will be very clear.

Then, in order to avoid confusion, try to use module.exports to export, and then use require to import.

Module export and import in ES

To be honest, the modules in es are very clear. However, there are some details that need to be clarified.

For example, export and export default, and when importing, import a from .., import {a} from .. are a bit confusing, so let’s start to sort them out.

export and export default

First let’s talk about these two exports. Next we’ll talk about their differences

Both export and export default can be used to export constants, functions, files, modules, etc.
In a file or module, there can be multiple exports and imports, but there is only one export default
Export through export, add { } when importing, export default is not required
export can directly export variablesExpression , export default does not work.

Let’s take a look at the code to verify it

testEs6Export.js

'use strict'
//导出变量
export const a = '100'; 
 //导出方法
export const dogSay = function(){ 
 console.log('wang wang');
}
 //导出方法第二种
function catSay(){
 console.log('miao miao'); 
}
export { catSay };
//export default导出
const m = 100;
export default m; 
//export defult const m = 100;// 这里不能写这种格式。

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index.js

//index.js
'use strict'
var express = require('express');
var router = express.Router();
import { dogSay, catSay } from './testEs6Export'; //导出了 export 方法 
import m from './testEs6Export'; //导出了 export default 
import * as testModule from './testEs6Export'; //as 集合成对象导出
/* GET home page. */
router.get('/', function(req, res, next) {
 dogSay();
 catSay();
 console.log(m);
 testModule.dogSay();
 console.log(testModule.m); // undefined , 因为 as 导出是 把 零散的 export 聚集在一起作为一个对象，而export default 是导出为 default属性。
 console.log(testModule.default); // 100
 res.send('恭喜你，成功验证');
});
module.exports = router;

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As can be seen from the above, the module system of ES6 does feel very flexible.

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!