是否自加減代碼順序會影響到代碼正確運行
document.onkeyup = function(event){
??????? event = event || window.event;
??????? for(var i=0;i<as.length;i++){
??????????? as[i].style.background = 'none';
??????? }
??????? if(event.keyCode == 38){
??????? ?if(index<=0){
??????????????? index = as.length;
??????????? }
??????? ?index--;
??????? ?as[index].style.background = '#ccc';
??????? }else if(event.keyCode == 40){
??????? ?index++;
??????? ?if(index>=as.length){
??????????????? index = 0;
??????????? }
??????? ?as[index].style.background = '#ccc';
??????? }else if(event.keyCode == 13 && index!=-1){
??????????? title.innerHTML = as[index].innerHTML;
??????????? menu.style.display = 'none';
??????????? index = -1;
??????? }
??? }
2017-02-13
你的代碼中自增和自減不會對該方法產生影響。只有在該變量如K=index++和K=++index就不一樣了。