make use of objects and numbers to make custom enums

enums.md

option a

i use uppercase to make more explicit the use of a constant

var directions = { UP : 0, RIGHT: 1, ... }

this.direction = directions.UP

option b

other option can is:

var DIRECTIONS = { 'up' : 0, 'right': 1, ... }

this.direction = DIRECTIONS['up']

which allows you to translate your number back to it's original string.