How to use modules in nodejs

In Node.js, modules are used to divide code and enhance maintainability. Export modules through module.exports and import modules through require(). Single values ​​(export keyword) or objects (module.exports) can be exported. Module paths can be absolute or relative. The module follows the singleton pattern and is cached after import. Dynamic modification can be achieved by changing module.exports.

How to use modules in Node.js

In Node.js, modules are independent files. Functions from other modules can be exported and imported. Using modules improves the maintainability and modularity of your code by organizing it into smaller reusable units.

How to export a module

To export a module, you can use the module.exports object. module.exports is a special object that represents the export value of the current module. To export a function, you assign it to module.exports:

// my-module.js
function sayHello() {
  console.log("Hello!");
}

module.exports = sayHello;

How to import a module

To import a module, you use require() function. require() The function receives the path or name of a module as a parameter and returns the object that exports the module:

// app.js
const sayHello = require("./my-module");

sayHello(); // 输出: "Hello!"

Importing and exporting multiple values

You can use the module.exports object to export multiple values, or you can use the export keyword to export a single value or variable:

// my-module.js
export function sayHello() {
  console.log("Hello!");
}

export const name = "John";

// app.js
import { sayHello, name } from "./my-module";

sayHello(); // 输出: "Hello!"
console.log(name); // 输出: "John"

Module path

Module paths can be absolute or relative to the current directory. If the path does not start with / or ./, Node.js will try to load the module from the node_modules directory.

Note:

• Module is a singleton mode, which means that multiple copies of the same module can only be exported once.
• When a module is imported, it will be compiled and cached in memory for quick access on future requests.
• You can dynamically modify the module's export value at runtime by modifying the module.exports object.

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