CODEWITHSUNDEEP
typescript
Adam Gawne-Cain
Adam Gawne-Cain

Reputation: 1710

Declare and Initialize Typescript class members

My class looks like this...

class MyClass {
    c: number;
    avg: number;
    diam: number;

    constructor(a: number, b: number) {
        this.c = Math.sqrt(a * a + b * b);
        this.avg = (a + b) / 2;
        this.diam = Math.abs(b - a);
    }
}

... but actually has more members that need declaring and initialising from the constructor arguments. I want to avoid the boilerplate of declaring the members outside the constructor and inside the constructor. Is there anyway to do that?

Upvotes: 0

Views: 424

Answers (2)

captain-yossarian from Ukraine
captain-yossarian from Ukraine

Reputation: 33101

You can do smth like that:


interface MathData {
    c: number;
    avg: number;
    diam: number;
}

const builder = (a: number, b: number):MathData => ({
    c: Math.sqrt(a * a + b * b),
    avg: (a + b) / 2,
    diam: Math.abs(b - a),
})


class MyClass {
    constructor(a: number, b: number) {
        Object.assign(this, builder(a, b));

    }
    calc(this: MathData) {
        this.avg // ok
        this.c // ok
        this.diam // ok
    }
}

Please, be aware that TypeScript does not track mutations.Hence, in order to get c or avg or diam you need to explicitly type this parameter. Playground

Upvotes: 1

Kelvin Schoofs
Kelvin Schoofs

Reputation: 8718

Yes, TypeScript supports something like that:

class MyClass {
    c: number = Math.sqrt(this.a * this.a + this.b * this.b);
    avg: number = (this.a + this.b) / 2;
    diam: number = Math.abs(this.b - this.a);

    constructor(public a: number, private readonly b: number) {
    }
}

That'll create a public field a and a private read-only field b. These are created before the initializers for the regular fields are executed, thus you can access those too.

Upvotes: 1

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