string_score.js

/*!
 * string_score.js: String Scoring Algorithm 0.1.10 
 *
 * http://joshaven.com/string_score
 * https://github.com/joshaven/string_score
 *
 * Copyright (C) 2009-2011 Joshaven Potter <yourtech@gmail.com>
 * Special thanks to all of the contributors listed here https://github.com/joshaven/string_score
 * MIT license: http://www.opensource.org/licenses/mit-license.php
 *
 * Date: Tue Mar 1 2011
 * Updated: Tue Jun 11 2013
*/

/**
 * Scores a string against another string.
 *  'Hello World'.score('he');     //=> 0.5931818181818181
 *  'Hello World'.score('Hello');  //=> 0.7318181818181818
 */
String.prototype.score = function(word, fuzziness) {

  // If the string is equal to the word, perfect match.
  if (this == word) return 1;

  //if it's not a perfect match and is empty return 0
  if( word == "") return 0;

  var runningScore = 0,
      charScore,
      finalScore,
      string = this,
      lString = string.toLowerCase(),
      strLength = string.length,
      lWord = word.toLowerCase(),
      wordLength = word.length,
      idxOf,
      startAt = 0,
      fuzzies = 1,
      fuzzyFactor;
  
  // Cache fuzzyFactor for speed increase
  if (fuzziness) fuzzyFactor = 1 - fuzziness;

  // Walk through word and add up scores.
  // Code duplication occurs to prevent checking fuzziness inside for loop
  if (fuzziness) {
    for (var i = 0; i < wordLength; ++i) {

      // Find next first case-insensitive match of a character.
      idxOf = lString.indexOf(lWord[i], startAt);
      
      if (-1 === idxOf) {
        fuzzies += fuzzyFactor;
        continue;
      } else if (startAt === idxOf) {
        // Consecutive letter & start-of-string Bonus
        charScore = 0.7;
      } else {
        charScore = 0.1;

        // Acronym Bonus
        // Weighing Logic: Typing the first character of an acronym is as if you
        // preceded it with two perfect character matches.
        if (string[idxOf - 1] === ' ') charScore += 0.8;
      }
      
      // Same case bonus.
      if (string[idxOf] === word[i]) charScore += 0.1; 
      
      // Update scores and startAt position for next round of indexOf
      runningScore += charScore;
      startAt = idxOf + 1;
    }
  } else {
    for (var i = 0; i < wordLength; ++i) {
    
      idxOf = lString.indexOf(lWord[i], startAt);
      
      if (-1 === idxOf) {
        return 0;
      } else if (startAt === idxOf) {
        charScore = 0.7;
      } else {
        charScore = 0.1;
        if (string[idxOf - 1] === ' ') charScore += 0.8;
      }

      if (string[idxOf] === word[i]) charScore += 0.1; 
      
      runningScore += charScore;
      startAt = idxOf + 1;
    }
  }

  // Reduce penalty for longer strings.
  finalScore = 0.5 * (runningScore / strLength  + runningScore / wordLength) / fuzzies;
  
  if ((lWord[0] === lString[0]) && (finalScore < 0.85)) {
    finalScore += 0.15;
  }
  
  return finalScore;
};