Import a Class from Another file using TypeScript

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Borislav Hadzhiev

Last updated: Mar 4, 2022

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Import a Class from Another file using TypeScript #

To import a class from another file in TypeScript:

  1. Export the class from file A, e.g. export class Employee {}.
  2. Import the class in file B as import { Employee } from './another-file'.
  3. Use the class in file B.

Here is an example of exporting a class from a file called another-file.ts.

another-file.ts
// 👇️ named export export class Employee { constructor(public id: number, public name: string, public salary: number) { this.id = id; this.name = name; this.salary = salary; } getSalary() { return this.salary; } }

Here is how we would import the Employee class in a file called index.ts.

index.ts
// 👇️ named import import { Employee } from './another-file'; const emp1 = new Employee(1, 'Tom', 100); console.log(emp1.name); // 👉️ "Tom" console.log(emp1.getSalary()); // 👉️ 100

Make sure to correct the path that points to the another-file module if you have to. The example above assumes that another-file.ts and index.ts are located in the same directory.

For example, if another-file.ts was located one directory up, you'd have to import as import {Employee} from '../another-file'.

We wrapped the name of the class in curly braces when importing it - this is called a named import.

TypeScript uses the concept of modules, in the same way that JavaScript does.

In order to be able to import a class from a different file, it has to be exported using a named or default export.

The example above uses a named export and a named import.

The main difference between named and default exports and imports is - you can have multiple named exports per file, but you can only have a single default export.

Let's look at an example of how we would import a class that was exported using a default export.

Here are the contents of another-file.ts.

another-file.ts
// 👇️ default export export default class Employee { constructor(public id: number, public name: string, public salary: number) { this.id = id; this.name = name; this.salary = salary; } getSalary() { return this.salary; } }

IMPORTANT: If you are exporting a variable (or an arrow function) as a default export, you have to declare it on 1 line and export it on the next. You can't declare and default export a variable on the same line.

And here is how we would import the class using a default import.

index.ts
// 👇️ default import import Employee from './another-file'; const emp1 = new Employee(1, 'Tom', 100); console.log(emp1.name); // 👉️ "Tom" console.log(emp1.getSalary()); // 👉️ 100

Notice that we didn't wrap the import in curly braces.

We could have also used a different name when importing the class, e.g. Foo.

index.ts
// 👇️ default import import Foo from './another-file'; const emp1 = new Foo(1, 'Tom', 100); console.log(emp1.name); // 👉️ "Tom" console.log(emp1.getSalary()); // 👉️ 100

This works, but is confusing and should be avoided.

In my experience, most real world codebases exclusively use named exports and imports, because they make it easier to leverage your IDE for autocompletion and auto-imports.
You also don't have to think about which members are exported with a default or named export.

You can also mix and match. Here is an example of a file that uses both a default and a named export.

another-file.ts
// 👇️ default export export default class Employee { constructor(public id: number, public name: string, public salary: number) { this.id = id; this.name = name; this.salary = salary; } getSalary() { return this.salary; } } // 👇️ named export export class Person { constructor(public name: string) { this.name = name; } getName() { return this.name; } }

And here is how you would import the two classes.

index.ts
// 👇️ default and named imports import Employee, { Person } from './another-file'; const emp1 = new Employee(1, 'Tom', 100); console.log(emp1.name); // 👉️ "Tom" console.log(emp1.getSalary()); // 👉️ 100 const person1 = new Person('James'); console.log(person1.getName()); // 👉️ "James"

We used a default import to import the Employee class and a named import to import the Person class.

Note that you can only have a single default export per file, but you can have as many named exports as necessary.

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