--description--

A vector can have one or more values represented by an ordered collection. Examples could be (x), (x, y), or (x, y, z).

--instructions--

Write a function that takes two vectors (represented as one-dimensional arrays) as input and computes their dot product. Your function should return null on invalid inputs such as vectors of different lengths or passing anything other than two vectors.

--hints--

dotProduct should be a function.

assert.equal(typeof dotProduct, 'function');

dotProduct() should return null.

assert.equal(dotProduct(), null);

dotProduct([1], [1]) should return 1.

assert.equal(dotProduct([1], [1]), 1);

dotProduct([1], [1, 2]) should return null.

assert.equal(dotProduct([1], [1, 2]), null);

dotProduct([1, 3, -5], [4, -2, -1]) should return 3.

assert.equal(dotProduct([1, 3, -5], [4, -2, -1]), 3);

dotProduct([3, 2, 1], [2, 4, 2], [5, 3, 1]) should return null.

assert.equal(dotProduct([3, 2, 1], [2, 4, 2], [5, 3, 1]), null);

dotProduct([ 0, 3, 6, 9, 12 ], [ 0, 4, 8, 12, 16 ]) should return 360.

assert.equal(dotProduct([ 0, 3, 6, 9, 12 ], [ 0, 4, 8, 12, 16 ]), 360);

--seed--

--seed-contents--

function dotProduct(...vectors) {

}

--solutions--

function dotProduct(...vectors) {
  if (!vectors || !vectors.length || vectors.length > 2 || vectors[0].length !== vectors[1].length) {
    return null;
  }
  const vectorLen = vectors[0].length;

  let prod = 0;
  let sum = 0;
  let j = vectorLen;
  let i = 2;
  // Sum terms
  while (j--) {
    i = 2;
    prod = 1;

    while (i--) {
      prod *= vectors[i][j];
    }
    sum += prod;
  }
  return sum;
}