Esegue un confronto tra 2 testi e ne restituisce la percentuale di similitudine

_similar.js

function similar_text (first, second, percent, limit) { 
  
  // eslint-disable-line camelcase
  //  discuss at: http://locutus.io/php/similar_text/
  // original by: Rafał Kukawski (http://blog.kukawski.pl)
  // bugfixed by: Chris McMacken
  // bugfixed by: Jarkko Rantavuori original by findings in stackoverflow (http://stackoverflow.com/questions/14136349/how-does-similar-text-work)
  // improved by: Markus Padourek (taken from http://www.kevinhq.com/2012/06/php-similartext-function-in-javascript_16.html)
  //   example 1: similar_text('Hello World!', 'Hello locutus!')
  //   returns 1: 8
  //   example 2: similar_text('Hello World!', null)
  //   returns 2: 0
  
  if (first === null ||
    second === null ||
    typeof first === 'undefined' ||
    typeof second === 'undefined') {
    return 0
  }
  first += ''
  second += ''
  var pos1 = 0
  var pos2 = 0
  var max = 0
  var firstLength = first.length
  var secondLength = second.length
  var p
  var q
  var l
  var sum
  for (p = 0; p < firstLength; p++) {
    for (q = 0; q < secondLength; q++) {
      for (l = 0; (p + l < firstLength) && (q + l < secondLength) && (first.charAt(p + l) === second.charAt(q + l)); l++) { // eslint-disable-line max-len
        // @todo: ^-- break up this crazy for loop and put the logic in its body
      }
      if (l > max) {
        max = l
        pos1 = p
        pos2 = q
      }
    }
  }
  sum = max;
  
  if( percent && limit > 0 ){
  
    var current = (sum * 200) / (firstLength + secondLength);
  
    if( current < limit )return current;
    
  }
  
  if (sum) {
    if (pos1 && pos2) {
      sum += similar_text(first.substr(0, pos1), second.substr(0, pos2))
    }
    if ((pos1 + max < firstLength) && (pos2 + max < secondLength)) {
      sum += similar_text(
        first.substr(pos1 + max, firstLength - pos1 - max),
        second.substr(pos2 + max,
        secondLength - pos2 - max))
    }
  }
  if (!percent) {
    return sum
  }
  return (sum * 200) / (firstLength + secondLength)
}