PHP's metaphone in JavaScript

module.exports = functionmetaphone (word, maxPhonemes) {
//  discuss at: https://locutus.io/php/metaphone/
// original by: Greg Frazier
// improved by: Brett Zamir (https://brett-zamir.me)
// improved by: Rafał Kukawski (https://blog.kukawski.pl)
//   example 1: metaphone('Gnu')
//   returns 1: 'N'
//   example 2: metaphone('bigger')
//   returns 2: 'BKR'
//   example 3: metaphone('accuracy')
//   returns 3: 'AKKRS'
//   example 4: metaphone('batch batcher')
//   returns 4: 'BXBXR'
const type = typeof word
if (type === 'undefined' || type === 'object' && word !== null) {
// weird!
returnnull
  }
// infinity and NaN values are treated as strings
if (type === 'number') {
if (isNaN(word)) {
      word = 'NAN'
    } elseif (!isFinite(word)) {
      word = 'INF'
    }
  }
if (maxPhonemes < 0) {
returnfalse
  }
  maxPhonemes = Math.floor(+maxPhonemes) || 0
// alpha depends on locale, so this var might need an update
// or should be turned into a regex
// for now assuming pure a-z
const alpha = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
const vowel = 'AEIOU'
const soft = 'EIY'
const leadingNonAlpha = newRegExp('^[^' + alpha + ']+')
  word = typeof word === 'string' ? word : ''
  word = word.toUpperCase().replace(leadingNonAlpha, '')
if (!word) {
return''
  }
const is = function (p, c) {
return c !== '' && p.indexOf(c) !== -1
  }
let i = 0
let cc = word.charAt(0) // current char. Short name because it's used all over the function
let nc = word.charAt(1) // next char
let nnc // after next char
let pc // previous char
const l = word.length
let meta = ''
// traditional is an internal param that could be exposed for now let it be a local var
const traditional = true
switch (cc) {
case'A':
      meta += nc === 'E' ? nc : cc
      i += 1
break
case'G':
case'K':
case'P':
if (nc === 'N') {
        meta += nc
        i += 2
      }
break
case'W':
if (nc === 'R') {
        meta += nc
        i += 2
      } elseif (nc === 'H' || is(vowel, nc)) {
        meta += 'W'
        i += 2
      }
break
case'X':
      meta += 'S'
      i += 1
break
case'E':
case'I':
case'O':
case'U':
      meta += cc
      i++
break
  }
for (; i < l && (maxPhonemes === 0 || meta.length < maxPhonemes); i += 1) { // eslint-disable-line no-unmodified-loop-condition,max-len
    cc = word.charAt(i)
    nc = word.charAt(i + 1)
    pc = word.charAt(i - 1)
    nnc = word.charAt(i + 2)
if (cc === pc && cc !== 'C') {
continue
    }
switch (cc) {
case'B':
if (pc !== 'M') {
          meta += cc
        }
break
case'C':
if (is(soft, nc)) {
if (nc === 'I' && nnc === 'A') {
            meta += 'X'
          } elseif (pc !== 'S') {
            meta += 'S'
          }
        } elseif (nc === 'H') {
          meta += !traditional && (nnc === 'R' || pc === 'S') ? 'K' : 'X'
          i += 1
        } else {
          meta += 'K'
        }
break
case'D':
if (nc === 'G' && is(soft, nnc)) {
          meta += 'J'
          i += 1
        } else {
          meta += 'T'
        }
break
case'G':
if (nc === 'H') {
if (!(is('BDH', word.charAt(i - 3)) || word.charAt(i - 4) === 'H')) {
            meta += 'F'
            i += 1
          }
        } elseif (nc === 'N') {
if (is(alpha, nnc) && word.substr(i + 1, 3) !== 'NED') {
            meta += 'K'
          }
        } elseif (is(soft, nc) && pc !== 'G') {
          meta += 'J'
        } else {
          meta += 'K'
        }
break
case'H':
if (is(vowel, nc) && !is('CGPST', pc)) {
          meta += cc
        }
break
case'K':
if (pc !== 'C') {
          meta += 'K'
        }
break
case'P':
        meta += nc === 'H' ? 'F' : cc
break
case'Q':
        meta += 'K'
break
case'S':
if (nc === 'I' && is('AO', nnc)) {
          meta += 'X'
        } elseif (nc === 'H') {
          meta += 'X'
          i += 1
        } elseif (!traditional && word.substr(i + 1, 3) === 'CHW') {
          meta += 'X'
          i += 2
        } else {
          meta += 'S'
        }
break
case'T':
if (nc === 'I' && is('AO', nnc)) {
          meta += 'X'
        } elseif (nc === 'H') {
          meta += '0'
          i += 1
        } elseif (word.substr(i + 1, 2) !== 'CH') {
          meta += 'T'
        }
break
case'V':
        meta += 'F'
break
case'W':
case'Y':
if (is(vowel, nc)) {
          meta += cc
        }
break
case'X':
        meta += 'KS'
break
case'Z':
        meta += 'S'
break
case'F':
case'J':
case'L':
case'M':
case'N':
case'R':
        meta += cc
break
    }
  }
return meta
}