Quick comparison between TypeScript and JavaScript, with a semantic error (sub method missing in Vector3 class). Used @ cacodaemon.de

gistfile1.txt

C:\Users\Caco\..>tsc TestTs.ts
C:/Users/Caco/../TestTs.ts(62,26)
: Cannot convert 'Vector2' to 'Vector3'

TestJs.js

function Vector2(x, y) {
  this.x = x ? x : 1;
	this.y = y ? y : 1;

	this.add = function(vector2) {
		return new Vector2(this.x + vector2.x, this.y + vector2.y);
	};

	this.sub = function(vector2) {
		return new Vector2(this.x - vector2.x, this.y - vector2.y);
	};

	this.dot = function(vector2) {
		return this.x * vector2.x + this.y * vector2.y
	};

	this.magnitude = function() {
		return Math.sqrt(this.x * this.x + this.y * this.y);
	};

	this.toString = function() {
		return 'X: ' + this.x + ' Y: ' + this.y;
	};
};

var vector2A = new Vector2(3, 3);
var vector2B = new Vector2(6, 6);
var vector2C = vector2A.add(vector2B);
var vector2D = vector2A.sub(vector2B);

console.log('Vector2 Add: ' + vector2A.add(vector2B));
console.log('Vector2 Sub: ' + vector2A.sub(vector2B));
console.log('Vector2 Dot: ' + vector2A.dot(vector2B));
console.log('Vector2 Magnitdue A: ' + vector2A.magnitude());
console.log('Vector2 Magnitdue B: ' + vector2B.magnitude());

function Vector3(x, y, z) {
	this.x = x ? x : 1;
	this.y = y ? y : 1;
	this.z = z ? z : 1;

	this.add = function(vector3) {
		return new Vector3(this.x + vector3.x, this.y + vector3.y, this.z + vector3.z);
	};

	this.dot = function(vector2) {
		return this.x * vector2.x + this.y * vector2.y + this.z * vector2.z;
	};

	this.magnitude = function() {
		return Math.sqrt(this.x * this.x + this.y * this.y + this.z * this.z);
	};

	this.toString = function() {
		return 'X: ' + this.x + ' Y: ' + this.y + ' Z: ' + this.z;
	};
};
Vector3.prototype = new Vector2();

var vector3A = new Vector3(3, 3, 3);
var vector3B = new Vector3(6, 6, 6);
var vector3C = vector3A.add(vector3B);
var vector3D = vector3A.sub(vector3B);

console.log('Vector3 Add: ' + vector3A.add(vector3B));
console.log('Vector3 Sub: ' + vector3A.sub(vector3B));
console.log('Vector3 Dot: ' + vector3A.dot(vector3B));
console.log('Vector3 Magnitdue A: ' + vector3A.magnitude());
console.log('Vector3 Magnitdue B: ' + vector3B.magnitude());

TestTs.js

var __extends = this.__extends || function (d, b) {
    function __() { this.constructor = d; }
    __.prototype = b.prototype;
    d.prototype = new __();
};
var Vector2 = (function () {
    function Vector2(x, y) {
        if (typeof x === "undefined") { x = 1; }
        if (typeof y === "undefined") { y = 1; }
        this.x = x;
        this.y = y;
    }
    Vector2.prototype.add = function (vector2) {
        return new Vector2(this.x + vector2.x, this.y + vector2.y);
    };
    Vector2.prototype.sub = function (vector2) {
        return new Vector2(this.x - vector2.x, this.y - vector2.y);
    };
    Vector2.prototype.dot = function (vector2) {
        return this.x * vector2.x + this.y * vector2.y;
    };
    Vector2.prototype.magnitude = function () {
        return Math.sqrt(this.x * this.x + this.y * this.y);
    };
    Vector2.prototype.toString = function () {
        return 'X: ' + this.x + ' Y: ' + this.y;
    };
    return Vector2;
})();
; ;
var vector2A = new Vector2(3, 3);
var vector2B = new Vector2(6, 6);
var vector2ADD = vector2A.add(vector2B);
var vector2SUB = vector2A.sub(vector2B);
var vector2DOT = vector2A.dot(vector2B);
console.log('Vector2 Add: ' + vector2ADD);
console.log('Vector2 Sub: ' + vector2SUB);
console.log('Vector2 Dot: ' + vector2DOT);
console.log('Vector2 Magnitdue A: ' + vector2A.magnitude());
console.log('Vector2 Magnitdue B: ' + vector2B.magnitude());
var Vector3 = (function (_super) {
    __extends(Vector3, _super);
    function Vector3(x, y, z) {
        if (typeof x === "undefined") { x = 1; }
        if (typeof y === "undefined") { y = 1; }
        if (typeof z === "undefined") { z = 1; }
        _super.call(this, x, y);
        this.z = z;
    }
    Vector3.prototype.add = function (vector3) {
        return new Vector3(this.x + vector3.x, this.y + vector3.y, this.z + vector3.z);
    };
    Vector3.prototype.dot = function (vector3) {
        return this.x * vector3.x + this.y * vector3.y + this.y * vector3.y;
    };
    Vector3.prototype.magnitude = function () {
        return Math.sqrt(this.x * this.x + this.y * this.y + this.z * this.z);
    };
    Vector3.prototype.toString = function () {
        return _super.prototype.toString.call(this) + ' Z: ' + this.z;
    };
    return Vector3;
})(Vector2);
var vector3A = new Vector3(3, 3, 3);
var vector3B = new Vector3(6, 6, 6);
var vector3ADD = vector3A.add(vector3B);
var vector3SUB = vector3A.sub(vector3B);
var vector3DOT = vector3A.dot(vector3B);
console.log('Vector3 Add: ' + vector3ADD);
console.log('Vector3 Sub: ' + vector3SUB);
console.log('Vector3 Dot: ' + vector3DOT);
console.log('Vector3 Magnitdue A: ' + vector3A.magnitude());
console.log('Vector3 Magnitdue B: ' + vector3B.magnitude());

TestTs.ts

class Vector2 {
  constructor (public x: number = 1, public y: number = 1) { }

	public add (vector2: Vector2) : Vector2 {
		return new Vector2(this.x + vector2.x, this.y + vector2.y);
	}

	public sub (vector2: Vector2) : Vector2 {
		return new Vector2(this.x - vector2.x, this.y - vector2.y);
	}

	public dot (vector2: Vector2) : number {
		return this.x * vector2.x + this.y * vector2.y;
	}

	public magnitude () : number {
		return Math.sqrt(this.x * this.x + this.y * this.y);
	}

	public toString() : string {
		return 'X: ' + this.x + ' Y: ' + this.y;
	}
};

var vector2A: Vector2 = new Vector2(3, 3);
var vector2B: Vector2 = new Vector2(6, 6);
var vector2ADD: Vector2 = vector2A.add(vector2B);
var vector2SUB: Vector2 = vector2A.sub(vector2B);
var vector2DOT: number = vector2A.dot(vector2B);

console.log('Vector2 Add: ' + vector2ADD);
console.log('Vector2 Sub: ' + vector2SUB);
console.log('Vector2 Dot: ' + vector2DOT);
console.log('Vector2 Magnitdue A: ' + vector2A.magnitude());
console.log('Vector2 Magnitdue B: ' + vector2B.magnitude());

class Vector3 extends Vector2 {
	constructor (x: number = 1, y: number = 1, public z: number = 1) { 
		super(x, y);
	}

	public add (vector3: Vector3) : Vector3 {
		return new Vector3(this.x + vector3.x, this.y + vector3.y, this.z + vector3.z);
	}

	public dot (vector3: Vector3) : number {
		return this.x * vector3.x + this.y * vector3.y + this.z * vector3.z;
	}

	public magnitude () : number {
		return Math.sqrt(this.x * this.x + this.y * this.y + this.z * this.z);
	}

	public toString () : string {
		return super.toString() + ' Z: ' + this.z; 
	}
}

var vector3A: Vector3 = new Vector3(3, 3, 3);
var vector3B: Vector3 = new Vector3(6, 6, 6);
var vector3ADD: Vector3 = vector3A.add(vector3B);
var vector3SUB: Vector3 = vector3A.sub(vector3B);
var vector3DOT: number = vector3A.dot(vector3B);

console.log('Vector3 Add: ' + vector3ADD);
console.log('Vector3 Sub: ' + vector3SUB);
console.log('Vector3 Dot: ' + vector3DOT);
console.log('Vector3 Magnitdue A: ' + vector3A.magnitude());
console.log('Vector3 Magnitdue B: ' + vector3B.magnitude());