What is the nodejs module search principle?

Node.js is a popular back-end development tool, and its module system is an important factor in its success. Node.js's module system has a simple but powerful principle, which is to let each file and module focus on one thing, and then use them when needed.

The module system of Node.js relies on the export and import of modules. Each .js file is an independent module and can export one of its interfaces for use by other modules.

When we use require('module-name') to import a module name, Node.js uses the following strategy to find it:

1. Find built-in modules

Node.js loads various built-in modules at startup, such as fs, http, etc. When you try to import a module using require("module-name") , the module is first looked up among the built-in modules.

If a built-in module is found and the module's name and path match, Node.js will return the module immediately. As a result, Node.js enables developers to use built-in modules quickly and efficiently.

2. Find third-party modules

If Node.js does not find a matching built-in module, the request will be passed to Node.js's module resolver to find it.

In Node.js, each module is located in its own file. Relative path imports mean that a module may need to reference other files in the file system.

When the parser encounters a relative path import, it uses the path used to parse the imported file and looks for the corresponding file in the file system.

Node.js will first look for the module in the directory where the current file is located, then iterate through the file's parent directory to find the module. This process will repeat until the module is found, or Node.js reaches the root of the file system.

If the parser finds a file matching the relative import path, the module is returned to require().

If the parser does not find the file, or finds an invalid file, require() will raise an Error.

3. Find Node.js modules

If Node.js is currently looking for a file, but another module tries to ask it to find a Node.js module, Node.js will interrupt the file. Find process and start looking for Node.js modules.

All core modules in Node.js are written using .js files and are located in specific directories of your Node.js installation. When you try to import a built-in Node.js module name in require(), Node.js will read the module and return it, ignoring any files or directories that match it.

4. Find global named modules

There are some global modules in Node.js, such as Buffer and process. These modules cannot be imported using require() in your app because Node.js does not traverse the file system to find them. They are often accessed through global objects, such as global.Buffer or global.process.

Summary

The module system of Node.js has a certain degree of flexibility and order, which allows you to only write closed modules without worrying that your code will conflict with other modules. Node.js's module system uses simple and clear principles: each file and module can focus on one thing, and can export an interface for other modules to use. Understanding the mechanics and search order of the Node.js module system can help you better understand the Node.js module system and how it works.

The above is the detailed content of What is the nodejs module search principle?. For more information, please follow other related articles on the PHP Chinese website!