无污染的原型扩展

    var iframe = document.createElement('iframe');
    iframe.style.display = 'none';
    document.body.appendChild(iframe);
    frames[frames.length - 1].document.write('<script>parent.Array2 = Array;<\/script>');
    document.body.removeChild(iframe);
    Array2.prototype.each = function() {
        alert('each');
    }
    var list = new Array2(1, 2, 3);
    alert(list.length)