Javascript hashCode function

hashCode.js

/**
 * Javascript hashCode function
 * This function is a modified version of 'Javascript implementation of Java’s String.hashCode() method'
 *
 * Modifications:
 * - Added comments
 * - Added string length caching
 * - Regular function instead of String.prototype
 * - Variable char (reserved word) is renamed to tmpChar.
 *
 * The original code can be found on this page:
 * http://werxltd.com/wp/2010/05/13/javascript-implementation-of-javas-string-hashcode-method/
 */

function hashCode(string) {

    var hash = 0;
    var tmpChar;
    var index;
    var stringLength = string.length

    // if the string es empty, then return immediately
    if (stringLength === 0) {

        return hash;

    }

    // loop the string
    for (index = 0; index < stringLength; index++) {

        // get character code at the index location
        tmpChar = string.charCodeAt(index);

        // left shift etc.
        hash = ((hash << 5) - hash) + tmpChar;

        // bitwise AND etc.
        hash = hash & hash; // Convert to 32bit integer

    }

    return hash;

}