[removed] Quickly lookup value in object (like we can with properties)

Question

I have an object that has pairs of replacement values used for simple encoding / decoding (not for security, just for a convenience; too complicated to explain it all here).

Answer 1

It's more efficient to loop just once beforehand to create a reverse map:

var str = "Hello World!",
    output = '',
    map = {
      "s":"d", "m":"e",
      "e":"h", "x":"l",
      "z":"o", "i":"r",
      "a":"w", "o":"!",
      "-":" "
    },
    reverseMap = {}

for (j in map){
  if (!Object.prototype.hasOwnProperty.call(map, j)) continue
  reverseMap[map[j]] = j
}

output = str.replace(/./g, function(c){
  return reverseMap[c] || reverseMap[c.toLowerCase()].toUpperCase()
})

console.log(output)

Instead of doing str.length * map.length, you'll do map.length + str.length operations.