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Nodejs modularization benefits: 1, code decoupling, can improve the reusability of the code; 2, can improve the maintainability of the code; 3, can improve the readability of the code; 4, can achieve on-demand loading; 5, can solve naming conflicts; 6, easy to manage dependencies.

This tutorial operating environment: windows7 system, nodejs version 12.19.0, DELL G3 computer.

What is modularization?

In the field of programming, modularization is a fixed rule to split a large file into independent and interdependent modules. Generally speaking, one js file can use data from another js file.

What are the benefits of modularization?

1. Code decoupling can improve the reusability of code.

2. it can improve the maintainability of the code.

3. It can improve the readability of the code

4. It can be loaded on demand.

5. Naming conflicts can be resolved

6. Facilitate the management of dependence

The generation of modularization also brings the module scope, which is similar to the function scope. The variables and methods defined in the custom module can only be accessed in the current scope. This access restriction effectively solves the problem of variable pollution.

Module specification

Modularization specifications are the rules that need to be followed when modularizing and combining code, such as:

What syntax format is used to reference the module

What syntax format is used in the module to expose members to the outside?

The benefits of modular specification: everyone follows the same modular specification to write code, which reduces the cost of communication, greatly facilitates the mutual call between various modules, and benefits others and self-interest.

Module specification category:

CommonJS specification: what is followed in nodejs is the commonjs specification.

ES6 Modularization Specification: (a common modularization specification for front and rear; it can be used in Node.js, Vue, React! )

CMD and AMD Modularization specifications (less used): CMD--sea.js, AMD-require.js

UMD is called the Universal Module definition Specification (Universal Module Definition), and it allows the same code module to run in a project that uses CommonJs, CMD, or even AMD at run time or compile time. It does not have its own proprietary specifications, it is a collection of CommonJs, CMD, AMD specifications in one.

Difference:

1. For dependent modules, AMD is executed in advance and CMD is deferred.

2. CMD favors relying on proximity, while AMD favors relying on the front.

Nodejs module classification

Built-in module-fs (file system module). Path (path module). Http (network operation module).

Const fs = require ("fs"); / / the basic module provided by node, which can be directly imported and used.

Custom module-.js file created by the user

Const m = require (". / js file name"); / / Note that it is the relative path and the suffix .js can be added or not.

Third-party module-A module developed by a third-party individual or team, usually called a package, that needs to be downloaded and imported before use

Const moment = require ('moment'); / / the import and export of the package module needs to be installed through the npm i moment command before use

Use the require () method to load the module

Note: when other modules are loaded using the require method, the code in the loaded module is executed

Export

There is a module object in each custom module, which stores the information related to the current module, and one of the properties, exports, can expose the module members for external use. When you load a module, you get an empty object that the module.exports property points to.

If you want to use the data in this module, you can add attribute values to the property module.exports for external use.

To simplify the code for sharing members, node provides an exports object. By default, exports and module.exports point to the same object.

Note: when you import a module using the require () method, the result of the import is always based on the object pointed to by module.exports.

Misunderstandings in the use of exports and module.exports exports = {username:'ls',gender:' male'} module.exports = exports;module.exports.age ='20 username:'ls',gender:' male / the result after import is {username:'ls',gender:' male', age:'20'} exports = {username:'ls',gender:' male'} module.exports.age ='20 female module.coach = exports / / the result after import is {username:'ls',gender:' male'} exports = {username:'ls',gender:' male'} exports = module.exports;module.exports.age ='20 players / the result after import is {age:'20'}

Therefore, try to use only one of these methods to avoid unnecessary trouble.

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