1-5 nodejs commonjs specification

CommonJs standard

node Based on CommonJs Standardized design , therefore node Is the composition of the module
Built-in module ：node Born to provide js Transfer
Three party modules ： Someone else wrote , We can base it on npm Install and use
Custom module ： Create your own modules

CommonJS The idea of modular design （AMD/CMD/ES6 module） It's all modular design ideas
1.CommonJS Regulations , every last JS It's all a single module （ Modules are private ： The values and functions involved 、 Variables are private , And others JS The contents of the document are not in conflict ）
2.CommonJS Allow methods in modules to call each other
B Module to call A Module method
A The module needs to be exported

CommonJS Give each module （ Every js） Built in variables are set in 、 attribute 、 Method
module: Represents the current module object
module.exports: This of the module “ attribute ” It is used to export the properties and methods of the module
exports: It's a built-in “ Variable ”, It is also used to export the properties and methods of the current module , Although and module.exports This is a thing , But the corresponding value is the same （module.exports = export） Values are objects
B Module needs to be imported
require:CommonJS Built in variables provided , Used to import modules （ In fact, import is module.exports Exposed things ）, Imported values are also （object type ） Of .

require It's a synchronous operation , It will be A Modules are executed from top to bottom , hold exports The corresponding heap memory is imported , So the result is an object .

CommonJs characteristic

1. All code runs within the scope of the module , Does not contaminate the global scope ( Every module is private , Everything in it is also private , No interference with other modules )
2. Modules can be loaded multiple times , But the command runs once on the first load , Then the run results are cached , Load later , Just read the cache results directly . To make the module run at a time , You must be clear about caching .
3. The order in which the modules are loaded , In the order it appears in the code
4.CommonJS The specification loading module is synchronous , in other words , Only load complete , To perform the following operations .