拖放函數時檢查目標元素是否已拖動元素ID function Drop() { if (this.querySelector('#' + dragItem.id)) { return; } this.append(dragItem)} snippet var p = document.getElementsByTagName('p');var choice = document.getElementsByClassName('choice');var dragItem = null;//console.log(p)for (var i of p) { i.addEventListener('dragstart', dragStart); i.addEventListener('dragend', dragEnd); i.style.background = i.id; //console.log(i)}function dragStart() { dragItem = this; setTimeout(() => this.style.display = "none", 0);}function dragEnd(ev) { setTimeout(() => this.style.display = "block", 0); dragItem = null;}for (va