foobar.js

const foobar = factors =>
  factors.map(factor => 
    factors.map(secondFactor => 
      factor * secondFactor
  )
);

var foobar = function(factors) {
  return factors.map(function(factor) {
    return factors.map(function (secondFactor) {
      return factor * secondFactor;
    })
  })
};