Detailed explanation of the loading rules of the require method in node.js

Loading rules of require method

1. Prioritize loading from cache
2. Core Modules
3. Modules in the form of paths
4. Third-party modules

1. Prioritize loading from cache

main.js: execute and load a.js module

require('./a')

a.js: executes and loads the b.js module, and outputs that a is loaded

require('./b')
console.log('a.js is loaded')

b.js: Output b is loaded

console.log('b.js is loaded')

result:

It can be seen that: main loads a.js, and then a does not print twice that a.js is loaded when loading b.js. Node will directly take out the exports value of the object from require.cache according to the passed id, and will not execute the module code again.

2. Core Modules

The essence of the core module is also a file. The core module file has been compiled into the binary file. We only need to load it according to the name. like:

• require('fs')
• require('http')

3. Path-based modules

The path-based module we are talking about is actually loading the JS file you wrote. There are four ways to load it.

var fooExports = require('./index') //Relative path, commonly used var fooExports = require('../index') //Relative path, commonly used var fooExports = require('/index') //Root directory, not commonly used var fooExports = require('D:/demo/index') //Root directory, not commonly used

4. Third-party modules

1. All third-party modules must be downloaded through npm
2. When using it, you can load it by requiring ('package name')
3. It is impossible for any third-party package to have the same name as a core module.

It is neither a core module nor a path-based module, or a third-party module. The loading method is as follows

Take var template = require('art-template') as an example:

• First find the node_modules directory in the directory where the current file is located
• Then find the main attribute in the file as follows
• The main attribute records the entry module of art-template
• Then load and use this third-party package, but in fact the final load is still the file
• If the package.json file does not exist or the entry module specified by main does not exist
• Then node will automatically find index.js in the directory, which means index.js will be used as a default option.
• If none of the above conditions are met, the node_modules directory in the parent directory will be searched.
• If the previous level does not have it, continue to search up the previous level.
• If the current disk root directory is still not found, an error message will be given: can not find module xxx

Third-party module search order: node_modules/art-template > package.json file > main property > index.js

This is the end of this article about the detailed explanation of the loading rules of the require method in node.js. For more relevant content about the loading rules of the node.js require method, please search for previous articles on 123WORDPRESS.COM or continue to browse the related articles below. I hope everyone will support 123WORDPRESS.COM in the future!