How to declare and import typescript interfaces in a separate file

Question

I want to define several interfaces in their own file in my typescript-based project, from which I'll implement classes for production as well as mocks for testing. However, I can't figure out what the correct syntax is. I've found plenty of tutorials on declaring interfaces and implementing them, but they all have a trivial implementation of both the interface and derived classes in the same file, which isn't very real-world. What's the right way to export and import the interfaces?

Answer 1

You need to export the interface from the file in which is defined and import it wherever you want to use it.

in IfcSampleInterface.ts:

export interface IfcSampleInterface {    key: string;    value: string; } 

In SampleInterface.ts

import { IfcSampleInterface } from './IfcSampleInterface'; let sampleVar: IfcSampleInterface; 

Answer 2

Use definition (d.ts) files and namespaces, no need to import/export modules this way. DefinitelyTyped project has guidance and huge number of examples how to do it.