How can I convert a TypeScript object to a plain object?

Something like this is simple and it works :

let plainObj;
try {
    plainObj = JSON.parse(JSON.stringify(obj));
} catch(e) {
    console.error(e)
}

You just need to destructure the object. Something like this: {...myObject}

You can use Object.assign():

class Point {
    private x: number;
    private y: number;

    constructor(x: number, y: number) {
        this.x = x;
        this.y = y;
    }

    getX(): number {
        return this.x;
    }

    getY(): number {
        return this.y;
    }
}

let p1 = new Point(4, 5);
let p2 = Object.assign({}, p1);

p1 is the class instance, and p2 is just { x: 4, y: 5 }.

And with the toPlainObj method:

class Point {
    private x: number;
    private y: number;

    constructor(x: number, y: number) {
        this.x = x;
        this.y = y;
    }

    getX(): number {
        return this.x;
    }

    getY(): number {
        return this.y;
    }

    toPlainObj(): { x: number, y: number } {
        return Object.assign({}, this);
    }
}

If this is something you need in more classes then you can have a base class which has this method:

class BaseClass<T> {
    toPlainObj(): T {
        return Object.assign({}, this);
    }
}

class Point extends BaseClass<{ x: number, y: number }> {
    private x: number;
    private y: number;

    constructor(x: number, y: number) {
        super();

        this.x = x;
        this.y = y;
    }

    getX(): number {
        return this.x;
    }

    getY(): number {
        return this.y;
    }
}