[SOLVED] How to create an alias of an interface from another module in typescript?

Issue

I have 2 typescript files.

commons.d.ts

module "commons" {
    interface IUser {
        name:string;
    }
}

main.ts

import commons = module("commons");
class User implements commons.IUser {
    name:string;
}

Since I will use commons.User a lot in the main.ts, I want to create an alias for it. For I change the code to:

import commons = module("commons");

import UserAlias = commons.IUser;

class User implements UserAlias {
    name:string;
}

But it throws error when compiling:

E:\WORKSPACE\app\typescripts>tsc main.ts
E:/WORKSPACE/app/typescripts/main.ts(3,27): The property 'IUser'
    does not exist on value of type 'commons'
E:/WORKSPACE/app/typescripts/main.ts(3,19): A module cannot be aliased
    to a non-module type

How to fix it?

Solution

To create an alias for an interface, you can extend it on a local interface:

I have tested this with:

commons.ts

export interface IUser {
    name: string;
}

app.ts

import commons = module("commons");

interface userAlias extends commons.IUser {
}

class User implements userAlias {
    name: string;
}

I have changed the commons.ts slightly because when you use External Modules don’t usually have a module declaration inside of them – the file is the module. The module declaration is used for internal modules.

You can read more about that in section 9.4 of the TypeScript language specification.

Answered By – Fenton

Answer Checked By – Jay B. (BugsFixing Admin)