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

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.