Require module in Node.js | Nodejs
Understanding require() in Node.js
The require() function allows you to include modules into your programs. You can import built-in Node.js modules, community-based modules (node_modules), and local modules.
How require() Works
The require() function returns an object, which references the value of module.exports for a given file. When invoked, it performs a sequence of tasks.
Important: require is a function that takes one argument called path in Node.js.
Module Resolution Order
The require() function searches for modules in the following order:
1. Built-in Node.js Modules
Core modules like fs, path, crypto, etc.
2. Modules in node_modules Folder
Community-installed packages like Express, Lodash, etc.
3. Local Modules (with Paths)
If the module name contains ./, /, or ../, it looks for the directory in the given path. Matches extensions: *.js, *.json, and *.node.
How to Use require() Function
Importing a Local Custom Module
Import modules from your project using relative or absolute paths:
const myLocalModule = require('./path/myLocalModules');Importing a JSON File
Directly require JSON files to get parsed data:
const jsonData = require('./path/jsonFile.json');Importing Built-in or npm Modules
Import Node.js built-in modules or packages from node_modules:
const crypto = require('crypto'); // Built-in
const express = require('express'); // From node_modulesComplete Example
Example demonstrating how to use the fs module to read a file:
const fs = require('fs');
fs.readFile('./myfile.txt', 'utf-8', (err, data) => {
if(err) {
throw err;
}
console.log('data: ', data);
});Explanation: In this example, the path is ./myfile.txt. The require('fs') loads Node.js's built-in file system module.
Common require() Patterns
Path Prefixes
./- Current directory../- Parent directory/- Absolute path- No prefix - node_modules
File Extensions
.js- JavaScript files.json- JSON files.node- Compiled addons- Extensions optional for .js
Types of Modules
| Module Type | Example | Use Case |
|---|---|---|
| Built-in | require('fs') |
Core Node.js functionality |
| Local | require('./myModule') |
Project-specific code |
| Third-party | require('express') |
Community packages |
| JSON | require('./config.json') |
Configuration data |
Key Points
- Module Caching: Modules are cached after the first require. Subsequent calls return the cached version
- Circular Dependencies: Be careful with circular dependencies as they can cause unexpected behavior
- Sync Operation:
require()is synchronous and blocks execution until the module is loaded - module.exports: Use
module.exportsto export functionality from your modules
Summary
The require() function is fundamental to Node.js module system, allowing you to load built-in modules, third-party packages, local files, and JSON configurations seamlessly.
Understanding how require() resolves modules helps you write better organized, modular Node.js applications. Remember that module resolution follows a specific order, and files are cached after the first require.