classList.js

/*
 * Minimal classList shim
 * Use with an Array.prototype.indexOf shim to support IE 8
 * Derived from work by Devon Govett
 * MIT LICENSE
 */


// NOT INTENDED FOR PRODUCTION USE.

if ( !("classList" in document.documentElement) ) {

  Object.defineProperty( Element.prototype, "classList", {
    get: function() {
      var self = this,
          rspaces = /\s+/g,
          implement;

      function classlist() {
        return self.className.trim().split(rspaces);
      }

      function update(fn) {
        return function(value) {
          var classes = classlist(),
            index = classes.indexOf(value);

          fn(classes, index, value);
          self.className = classes.join(" ");

          implement.length = classes.length;
        };
      }

      implement = {

        length: (function() {
          return classlist().length;
        })(),

        add: update(function(classes, index, value) {
          ~index || classes.push(value);
        }),

        remove: update(function(classes, index) {
          ~index && classes.splice(index, 1);
        }),

        toggle: update(function(classes, index, value) {
          ~index ? classes.splice(index, 1) : classes.push(value);
        }),

        contains: function(value) {
          return !!~classlist().indexOf(value);
        },

        item: function(i) {
          return classlist()[i] || null;
        }
      };

      return implement;
    }
  });
}

var element = document.getElementById("test");

console.log( element.classList.length );

element.classList.add("ponies");

console.log( element.classList.length );