Inner product by JavaScript (ES2015)

dot.js

function dot(a, b) {
  const len = Math.max(a.length, a.length);

  let zeros = new Array(len).fill(0);

  let ret;

  ret = zeros.reduce((p, c, i) => {
    const itemA = a[i] || 0;
    const itemB = b[i] || 0;
    const val = itemA * itemB;
    return p + val;
  }, 0);

  return ret;
}

const vecA = [1, 2, 3];
const vecB = [4, 5, 6];

vec = dot(vecA, vecB);

console.log(vec); // => 32