Implement getters and setters to ease access to private members of Vector.

vector.js

/*global console: true */
"use strict";
/*
A vector type
Write a constructor Vector that represents a vector in two-dimensional
space. It takes x and y parameters (numbers), which it should save to
properties of the same name.
Give the Vector prototype two methods, plus and minus, that take another vector as a parameter and return a new vector that has the sum
or difference of the two vectors’ (the one in this and the parameter) x
and y values.
Add a getter property length to the prototype that computes the length
of the vector—that is, the distance of the point (x, y) from the origin (0,
0)
 */

var Vector = function(x, y) {
    var _x = x,
        _y = y;
    this.getX = function() { return _x;};
    this.getY = function() { return _y;};
    this.setX = function(x) { _x = x;};
    this.setY = function(y) { _y = y;};
};

Vector.prototype.plus = function(vect){
    return new Vector(this.x + vect.x, this.y + vect.y);
};

Vector.prototype.minus = function(vect){
    return new Vector(this.x - vect.x, this.y - vect.y);
};

Vector.prototype.print = function(){
    console.log("(" + this.x + ", " + this.y + ")");
};

Object.defineProperty(Vector.prototype, "length", {
    get: function () { return Math.sqrt(this.x*this.x + this.y*this.y); }
});

Object.defineProperty(Vector.prototype, "x", {
    set: function (x) {this.setX(x);},
    get: function () {return this.getX();}
});

Object.defineProperty(Vector.prototype, "y", {
    set: function (y) {this.setY(y);},
    get: function () {return this.getY();}
});

(new Vector(1, 2)).plus(new Vector(2, 3)).print();
// → Vector{x: 3, y: 5}
(new Vector(1, 2)).minus(new Vector(2, 3)).print();
// → Vector{x: -1, y: -1}
console.log(new Vector(3, 4).length);
// → 5
var test = new Vector(1, 5);
test.x = 30;
test.a = 52;
test.print();