access-nyc-patterns/src/utilities/autocomplete/jaro-winkler.js

User Interface Patterns for Benefits Access

/**
 * JaroWinkler function.
 * https://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance
 * @param {string} s1 string one.
 * @param {string} s2 second string.
 * @return {number} amount of matches.
 */
function jaro(s1, s2) {
  let shorter;
  let longer;

  [longer, shorter] = s1.length > s2.length ? [s1, s2] : [s2, s1];

  const matchingWindow = Math.floor(longer.length / 2) - 1;
  const shorterMatches = [];
  const longerMatches = [];

  for (let i = 0; i < shorter.length; i++) {
    let ch = shorter[i];
    const windowStart = Math.max(0, i - matchingWindow);
    const windowEnd = Math.min(i + matchingWindow + 1, longer.length);
    for (let j = windowStart; j < windowEnd; j++)
      if (longerMatches[j] === undefined && ch === longer[j]) {
        shorterMatches[i] = longerMatches[j] = ch;
        break;
      }
  }

  const shorterMatchesString = shorterMatches.join('');
  const longerMatchesString = longerMatches.join('');
  const numMatches = shorterMatchesString.length;

  let transpositions = 0;
  for (let i = 0; i < shorterMatchesString.length; i++)
    if (shorterMatchesString[i] !== longerMatchesString[i])
      transpositions++;
  return numMatches > 0
    ? (
        numMatches / shorter.length +
        numMatches / longer.length +
        (numMatches - Math.floor(transpositions / 2)) / numMatches
      ) / 3.0
    : 0;
}

/**
 * @param {string} s1 string one.
 * @param {string} s2 second string.
 * @param {number} prefixScalingFactor
 * @return {number} jaroSimilarity
 */
export default function(s1, s2, prefixScalingFactor = 0.2) {
  const jaroSimilarity = jaro(s1, s2);

  let commonPrefixLength = 0;
  for (let i = 0; i < s1.length; i++)
    if (s1[i] === s2[i])
      commonPrefixLength++;
    else
      break;

  return jaroSimilarity +
    Math.min(commonPrefixLength, 4) *
    prefixScalingFactor *
    (1 - jaroSimilarity);
}