An implementation of Soundex algorithm in JavaScript. (Introduction to Information Retrieval)

soundex.js

var isAlpha = function(s) { return /^[a-zA-Z]+$/.test(s) }
 
var soundex = function(s) {
    if(s==='')
      return '0000'
      
    const
      head = s[0].toLowerCase(),
      tail = s.substr(1).toLowerCase()
 
    if(!isAlpha(head))
      return soundex(tail)
 
    const
      dict= {
        a: '', e: '', i: '', o: '', u: '', y:'', h:'', w:'',
        b: 1, f: 1, p: 1, v: 1,
        c: 2, g: 2, j: 2, k: 2, q: 2, s: 2, x: 2, z: 2,
        d: 3, t: 3,
        l: 4,
        m: 5, n: 5,
        r: 6
      },
      t=tail.split(''),
      r= head + t
          .map(function (v, i, array) { return dict[v] })
          .filter(function (v, i, array) {return i===0? v !== dict[head] : v !== array[i-1]})
          .join('')
 
    return (r.toUpperCase() + '000').slice(0, 4)
}