TypeScript : Copy objects with properties that matches

Question

I want to create a new object only with the properties that i need.

Example:


interface Foo {
    a: string;
    c: string;
}
interface Doo {
    a: string;
    h: number;
    c: string;
}

const objFoo = {} as Foo;
const objDoo = {} as Doo;

objFoo = {}
objDoo = { a: 'hi', h: 1, c: 'gray' }


objFoo = objDoo // only with the properties that matches with properties of objFoo

//output expected
objFoo { a: 'hi', c: 'gray' }

i tried with object.assign(objFoo,objDoo), but doens't work. please help

You can't do this with typescript, and you also shouldn't use as Foo/Doo because the empty object does not match that interface. — Evert
– Evert, Commented Jul 30, 2020 at 20:37
nice, and the way to solve this problem is initializing the object properties ? — Renan Duarte
– Renan Duarte, Commented Jul 30, 2020 at 20:39
You should just explicitly specify which properties you want to copy, or you keep an array with all properties you want to copy and loop through it. — Evert
– Evert, Commented Jul 30, 2020 at 20:40

andsilver · Accepted Answer · 2020-07-30 21:39:46Z

1

If you switch to classes and have very verbose constructors, it can be done. Its not pretty, and I'm not sure I'd recommend it though.

Working stackblitz, see the console log of the objects: https://stackblitz.com/edit/angular-vqs81k

export class Foo {
    a: string;
    c: string;
    constructor(kwargs?: Partial<Foo>) {
        if (kwargs) {
            this.a = kwargs.a;
            this.c = kwargs.c;
        }

    }
}

export class Doo {
    a: string;
    h: number;
    c: string;
    constructor(kwargs?: Partial<Doo>) {
        if (kwargs) {
            this.a = kwargs.a;
            this.h = kwargs.h;
            this.c = kwargs.c;
        }

    }
}

let objDoo = new Doo({ a: 'hi', h: 1, c: 'gray' });

let objFoo = new Foo(objDoo);

console.log(objDoo);
console.log(objFoo);

edited Jul 30, 2020 at 21:39

andsilver

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answered Jul 30, 2020 at 20:48

cjd82187

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