JavaScript implementation of hashcode

hashcode.js

/**
 * Returns a hash code for a string.
 * (Compatible to Java's String.hashCode())
 *
 * The hash code for a string object is computed as
 *     s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
 * using number arithmetic, where s[i] is the i th character
 * of the given string, n is the length of the string,
 * and ^ indicates exponentiation.
 * (The hash value of the empty string is zero.)
 *
 * @param {string} s a string
 * @return {number} a hash code value for the given string.
 */
hashCode = function(s) {
  var h = 0, l = s.length, i = 0;
  if ( l > 0 )
    while (i < l)
      h = (h << 5) - h + s.charCodeAt(i++) | 0;
  return h;
};

hashCode = s => s.split('').reduce((a,b)=>{a=((a<<5)-a)+b.charCodeAt(0);return a&a},0)

function hashCode(s) {
    for(var i = 0, h = 0; i < s.length; i++)
        h = Math.imul(31, h) + s.charCodeAt(i) | 0;
    return h;
}