nodejs import usage

In Node.js, we can use the module mechanism to separate code and make the program more modular. The module loading method of Node.js is very simple. You can load modules through the require() function. However, if we wish to introduce functions or variables of another module into one module, we can use the import statement. This article will introduce the usage of import in Node.js.

1. Using import in Node.js

In Node.js, using the import statement needs to follow the following rules:

(1) Node. js must be executed in script mode of ECMAScript 6 or higher
(2) To use the import statement, Babel support must be enabled through the .babelrc configuration file or through command line parameters

The following is a simple Example to demonstrate how to use the import statement in Node.js:

// demo.js
import { add } from './math.js';

console.log(add(1, 2));

// math.js
export function add(a, b) {
  return a + b;
}
export function mul(a, b) {
  return a * b;
}

In the above example, we used the ES6 import statement in the demo.js file and imported it from the math.js file. add function. In the math.js file, we use the ES6 export keyword to export the add function and mul function for use by other modules.

2. Notes

(1) Variables exported by default cannot be imported using the dot symbol (.) operation

When we use the default export, You cannot use the dot notation (.) for import. For example, there is the following default export in math.js:

export default function hello() {
  console.log('Hello World!');
}

We can use it like this in other modules:

import hello from './math.js';
hello(); // Output: Hello World!

(2) Named exported variables can be operated using the dot symbol (.) Import

When we use named export, we can use the dot symbol (.) operation to import. For example, there is the following named export in math.js:

export const PI = 3.1415926;
export function add(a, b) {
  return a + b;
}

We can use it like this in other modules:

import { PI, add } from './math.js';
console.log(PI); // Output: 3.1415926
console.log(add(1, 2)); // Output: 3

(3) The import statement must be placed at the head of the file

In the ES6 module system, the import statement must be placed at the head of the file and cannot be placed after other statements. Otherwise, an error will be reported.

(4) The priority of import is higher than require

When using import and require to share the same module, the priority of import is higher than require. That is to say, if both the import statement and the require function are used in the same module, the module imported by the import statement will be loaded and executed first.

3. Conclusion

Through the import statement, we can easily use the modularity feature of ES6 in Node.js to achieve code separation and reuse. There are some rules and caveats to be aware of when using the import statement in Node.js, but as long as you follow these rules, you can use the import statement easily.

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