Javascript Help

Question

Hi i would simply like to know what this means:

function flipString(aString) {
 var last = aString.length - 1;
 var result = new Array(aString.length)
 for (var i = last; i >= 0; --i) {
  var c = aString.charAt(i)
  var r = flipTable[c]
  result[last - i] = r != undefined ? r : c
 }
 return result.join('')
}

Answer 1

It looks like some sort of encryption / obfuscation. Without knowing what filpTable looks like it's hard to say.

function flipString(aString) {
 var last = aString.length - 1;

 // Create a new array with the length of the string
 var result = new Array(aString.length)

 // Walk through the string backwards
 for (var i = last; i >= 0; --i) {
  // Get the current character
  var c = aString.charAt(i)

  // Find the associated character in the flipTable
  var r = flipTable[c]

  // If the character wasn't in the flip table, use it as-is, else use the one we found
  // Store as (last-i) instead of (i) so it comes out backwards
  result[last - i] = r != undefined ? r : c
 }

 // Return the result as a string instead of an array
 return result.join('')
}

Answer 2

It walks through a string from the first character to the last, whilst storing the character found at each index in an array. For each character, if the array "flipTable" has an entry associated with it, it uses the flipTable entry rather than the character. The resultant array is then joined with '' to make a string.

In simpler terms, it reverses a string whilst simultaneously changing every character that is a key for flipTable to the entry associated with it. Why you'd do this, I have no idea without context.

Answer 3

Looks like a simple substitution cipher implementation. flipTable contains the substitution alphabet, and the function steps through each character in the string and replaces it with its counterpart from that alphabet.