package. json

6、package.json

（1）node_modules Folder problems

Too many folders and files are broken , When we copy the whole project to others ,, The transmission speed will be very slow .

Complex module dependencies need to be documented , Make sure that the version of the module is consistent with the current version , Otherwise, the current project operation will report an error

（2）package.json Role of documents

Project description file , Record the current project information , For example, project name 、 edition 、 author 、github Address 、 What third-party modules the current project depends on .

Use npm init -y Command to generate .

（3） Project dependence

In the development stage and online operation stage of the project , All need to rely on third-party packages , It's called project dependency

Use npm install The files downloaded by the package name command will be added to by default package.json Of documents dependencies Field

 {
    "dependencies": {
        "jquery": "^3.3.1“
    }
 } 

（4） Development depends on

In the development phase of the project, we need to rely on , Third party package that does not need to be relied on in the online operation stage , It's called development dependency

Use npm install Package name --save-dev Command add package to package.json Of documents devDependencies Field

 {
    "devDependencies": {
        "gulp": "^3.9.1“
    }
 } 

（5）package-lock.json Role of documents

Lock the version of the package , Make sure you don't have problems with the different versions of the package when you download it again

Faster downloads , Because the tree structure of the third-party package that the project depends on and the download address of the package have been recorded in this file , When reinstalling, just download it , There's no need to do extra work

7、Node.js Module loading mechanism in

（1） Module search rules - When a module has a path but no suffix

require Methods search the module according to the module path , If it's a full path , Directly introduce modules .

If the module suffix is omitted , Find the same name first JS Find the same name for the document JS Folder

If you find a folder with the same name , Look for... In the folder index.js

If there is no index.js I'll go to... In the current folder package.json Find in the file main Entry file in options

If the specified entry file does not exist or does not exist, an error will be reported , Module not found

（2） Module search rules - When the module has no path and no suffix

Node.js Assume it's a system module

Node.js Will go to node_modules In the folder

First of all, see if there is a JS file

See if there is a folder with that name

If it's a folder, see if there is index.js

without index.js See... In this folder package.json Medium main Option to determine the module entry file

Otherwise, we can't find the wrong report