aSapien

function compose(func, ...funcs) {
  return function(...args) {
      return funcs.length > 0
        ? compose(...funcs)(func(...args))
        : func(...args)
  }
}

// Or, in a more compact version:
const compose = (func, ...funcs) => (...args) =>

aSapien

var mat = [ 
    [1, 2, 3, 4], 
    [5, 6, 7, 8], 
    [9, 10, 11, 12], 
    [13, 14, 15, 16]
];

var DIRECTIONS = {
    FORWARD: 1,
    BACKWARD: -1