6.1 A Vector Type (Eloquent JavaScript Solutions)

6-1 Eloquent Javascript Solutions.js

class Vec {
  constructor (x, y) {
    this.x = x;
    this.y = y;
  }
  plus(v) {
    return new Vec(this.x + v.x, this.y + v.y);
  }
  minus(v) {
    return new Vec(this.x - v.x, this.y - v.y);
  }
  get length() {
    return Math.sqrt(Math.pow(this.x, 2) + Math.pow(this.y, 2));
  }
}

console.log(new Vec(1, 2).plus(new Vec(2, 3)));
// → Vec{x: 3, y: 5}
console.log(new Vec(1, 2).minus(new Vec(2, 3)));
// → Vec{x: -1, y: -1}
console.log(new Vec(3, 4).length);
// → 5

The Secret Life of Objects

6.1 A Vector Type

Write a class Vec 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 Vec 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’ (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).

Hints

Look back to the Rabbit class example if you’re unsure how class declarations look.

Adding a getter property to the constructor can be done by putting the word get before the method name. To compute the distance from (0, 0) to (x, y), you can use the Pythagorean theorem, which says that the square of the distance we are looking for is equal to the square of the x-coordinate plus the square of the y-coordinate. Thus, √(x2 + y2) is the number you want, and Math.sqrt is the way you compute a square root in JavaScript.