// Minimum length of Soundex keys.

var minLength = 4

// Soundex values belonging to characters.

// This map also includes vowels (with a value of 0) to easily distinguish

// between an unknown value or a vowel.

var map = {}

map.a = map.e = map.i = map.o = map.u = map.y = 0

map.b = map.f = map.p = map.v = 1

map.c = map.g = map.j = map.k = map.q = map.s = map.x = map.z = 2

map.d = map.t = 3

map.l = 4

map.m = map.n = 5

map.r = 6

/**

 * Get the soundex key from a given value.

 *

 * @param {string} value

 * @param {number} [maxLength=4]

 * @returns {string}

 */

function soundex(value, maxLength) {

  var lowercase = String(value).toLowerCase()

  /** @type {Array.<string|number>} */

  var results = []

  var index = -1

  /** @type {string} */

  var character

  /** @type {number} */

  var previous

  /** @type {number} */

  var phonetics

  while (++index < lowercase.length) {

    character = lowercase.charAt(index)

    phonetics = map[character]

    if (index === 0) {

      // Initial letter

      results.push(character.toUpperCase())

    } else if (phonetics && phonetics !== previous) {

      // Phonetics value

      results.push(phonetics)

    } else if (phonetics === 0) {

      // Vowel

      phonetics = null

    } else {

      // Unknown character (including H and W)

      phonetics = previous

    }

    previous = phonetics

  }

  return pad(results.join('')).slice(0, maxLength || minLength)

}

/**

 * Pad a given value with zero characters. The function only pads four characters.

 *

 * @param {string} value

 * @returns {string}

 */

function pad(value) {

  var length = minLength - value.length

  var index = -1

  while (++index < length) {

    value += '0'

  }

  return value

}

console.log(

  soundex('Joe'),

  soundex('Smith'),

  soundex('Ed'), 

  soundex('Vilowat')

)