window.onload = function(){
                
                document.querySelector("p").onscroll = function(){
                    // 滑动的距离
                    var n = this.scrollTop; //2304
                    // 滑动元素的总高度
                    var v = this.scrollHeight; //2704
                    // 可见高度
                    var c = this.clientHeight; //400
                    
                    if(v-n == c){
                        document.querySelector("input").disabled = false;
                        document.querySelector("button").disabled = false;
                    }
                }
            }