good old prototypal inheritance done without leaks

inherit.js

var inherit = (function () {
  function Constructor() {
    // always reassign the initial
    // prototype to avoid problems
    // in jurassic engines
    Constructor.prototype = cp;
  }
  // original prototype
  var cp = Constructor.prototype;
  // the inherit function
  return function (object) {
    // assign it once
    Constructor.prototype = object;
    // and drop any reference once constructoed
    return new Constructor;
  };
}());

if you need classes like inheritance that works down to IE6 or lower but it's compatible with modern and future standards have a look at es-class