TypeScript: Add properties to an object’s prototype

When you try to add a property to an object’s prototype using TypeScript, you’ll get a compiler error inside Visual Studio.

	// Module
	module Shapes {
	// Class
	export class Point implements IPoint {
	// Constructor
	constructor (public x: number, public y: number) { }
	// Instance member
	getDist() { return Math.sqrt(this.x * this.x + this.y * this.y); }
	// Static member
	static origin = new Point(0, 0);
	}
	Point.prototype.getCoordinates = function () { }
	}

view raw Shapes.ts hosted with ❤ by GitHub

Too get rid of the error message, you’ll have to create an interface on the prototype object type and declare the function there:

	interface Object {
	getCoordinates(): any;
	}
	// Module
	module Shapes {
	// Class
	export class Point implements IPoint {
	// Constructor
	constructor (public x: number, public y: number) { }
	// Instance member
	getDist() { return Math.sqrt(this.x * this.x + this.y * this.y); }
	// Static member
	static origin = new Point(0, 0);
	}
	Point.prototype.getCoordinates = function () { }
	}

view raw Shapes.ts hosted with ❤ by GitHub