It depends on what environment you're running in. In a web browser you simply need to make sure that file1.js is loaded before file2.js:

<script src="file1.js"></script>
<script src="file2.js"></script>

In node.js, the recommended way is to make file1 a module then you can load it with the require function:

require('path/to/file1.js');

It's also possible to use node's module style in HTML using the require.js library.

You can simply do this:

user.js

class User {
  //...
}

module.exports = User //  Export class

server.js

const User = require('./user.js')

let user = new User()

This is called CommonJS module.

ES Modules

Since Node.js version 14 it's possible to use ES Modules with CommonJS. Read more about it in the ESM documentation.

user.mjs ( extension is important)

export default class User {}

server.mjs

import User from './user.mjs'

let user = new User()

There is no export default class in JavaScript. What you can do is write your JS file like this. myClass/index.js

"use strict";
class MyClass {
  hello(name) {
    console.log(`Hello ${name}`);
  }

}
exports.default = MyClass;

Create a Type definitions for it. myClass/index.d.ts

export default class MyClass {
  hello(name: string): void;
}

You can then import it into your TypeScript like this.

/// <reference path="./myClass/index.d.ts" />
import MyClass from "./myClass";

const my = new MyClass();
my.hello("Stack Overflow");

You are only importing the class, but not making an instance of the class

Try

var myInstance = new Example()
myInstance.test()

Since you are trying to import a module it will be better if you try exporting your classes as a module as well, like this, module.exports = { h1, hello }; and then you can import it in your other file like this, const { h1, hello } = require("./temp");. Hope this solves your problem