A Vector Class in Javascript

Question

I'm trying to implement a vector object instantiated like below...

var a = new Vector([1,2,3]);
var b = new Vector ([2,2,2]);

...and when I do a math operation I need something like this...

a.add(b); // should return Vector([3,4,5])

...but my code below returns me just an array

function Vector(components) {
  // TODO: Finish the Vector class.
  this.arr = components;
  this.add = add;
}

function add(aa) {
  if(this.arr.length === aa.arr.length) {
    var result=[];
    for(var i=0; i<this.arr.length; i++) {
       result.push(this.arr[i]+aa.arr[i]);
    }
    return result;
  } else {
    return error;
  }
}

Please help me out here. Thank you!

Answer 1

Perhaps it is simpler to extend javascript's native Array, so that there is no need for keeping around an extra Vector.arr property. Here is a simple implementation called for learning purposes that boils down to this, in modern JS:

class Vector extends Array {
  // example methods
  add(other) {
    return this.map((e, i) => e + other[i]);
  }
}

// example usage
let v = new Vector(1, 2, 3);
console.log(v.add(v));

This class inherits Array's constructor. Note passing in a single value creates an empty Array of that length and not a length 1 Array. Vector would require a super call in the constructor to inherit exotic Array behavior, such as having a special length property, but this shouldn't be needed for a math vector of fixed length. You can include fancier constructor behavior here, such as being able to construct from an Array as input.

Answer 2

The solution by James looks good but it's a bit old-fashioned in my opinion. Here is a way to solve the problem in modern ES6 Javascript Classes.

class Vector {
  constructor(arr) {
    this.arr = arr;
  }
  add(otherVector) {
    const oa = otherVector.arr;
    if (this.arr.length === oa.length) {
      let res = []
      for(let key in this.arr) {
        res[key] = this.arr[key] + oa[key]
      }
      return new Vector(res)
    }
  }
}