TypeScript - interface getter

In this article, we would like to show how in TypeScript create getter in interface and later implement it.

W TypeScript nie jest możliwe dodawanie getterów bezpośrednio do interfejsu. W interfejsie można określić tylko właściwość tylko do odczytu.

Quick solution:

interface Interface {
    readonly getter: string;
}

class Implementation implements Interface {
    get getter(): string {
        return 'Some value here ...';
    }
}

Practical example

interface Square {
    readonly name: string;

    readonly x: number;
    readonly y: number;
}

class LocalSquare implements Square {

    public constructor(private _name: string, private _x: number = 0, private _y: number = 0) {
        // Nothing here ...
    }

    get name(): string {
        return this._name;
    }

    get x(): number {
        return this._x;
    }

    get y(): number {
        return this._y;
    }
}

let a = new LocalSquare('A', 1, 2);

console.log(`${a.name}(${a.x}, ${a.y})`);

Complilation and running:

$ tsc --target ES5 Script.ts
$ node Script.js

Output:

A(1, 2)

Run it online here.

Notes:

• to enable getters support --targer ES5 parameter during complilation is necessary (check full list of targets here)
• readonly keyword in interface is optional

References

1. Readonly properties - Microsoft Docs