<script>

    function baseClass()

    {

        this.showMsg = function()

        {

            alert("baseClass::showMsg");

        }

    }

    function extendClass()

    {

        this.showMsg =function ()

        {

            alert("extendClass::showMsg");

        }

    }

    extendClass.prototype = new baseClass();

    var instance = new extendClass();

    var baseinstance = new baseClass();

    baseinstance.showMsg.call(instance);

    //显示baseClass::showMsg

</script>