Question

第二部分由于某种原因读取null。它在第一部分工作。

window.onload = function() {
var div = document.createElement("div");
div.innerHTML = '<img alt="pickle" src="images/pickle">';
div.style.visibility = "visible";
div.style.position = "absolute";
div.style.zIndex = "3";
div.className = "jack";
document.body.appendChild(div);

第二部分

document.onmousemove=function(e){
  var x, y;
  if (e) {x=e.clientX; y=e.clientY;} 
  else {x=event.clientX;y=event.clientY;}
  var jack = document.getElementById('jack');
  jack.style.top=y+'px';
  jack.style.left=x+50+'px';
}};

＆＃13;

window.onload = function() {
var div = document.createElement("div");
div.innerHTML = '<img alt="pickle" src="images/pickle">';
div.style.visibility = "visible";
div.style.position = "absolute";
div.style.zIndex = "3";
div.className = "jack";
document.body.appendChild(div);

document.onmousemove=function(e){
  var x, y;
  if (e) {x=e.clientX; y=e.clientY;} 
  else {x=event.clientX;y=event.clientY;}
  var jack = document.getElementByClassName('jack');
  jack.style.top=y+'px';
  jack.style.left=x+50+'px';
  }};

＆＃13;

<html>
<head>
</head>
<body>
</body>
</html>

＆＃13;

Answer 1

您正在定位#jack，但该元素没有ID，只有一个类。将以下内容添加到您要创建元素的代码部分。

div.id = "jack";

var div = document.createElement("div");
div.innerHTML = '<img alt="pickle" src="images/pickle">';
div.style.visibility = "visible";
div.style.position = "absolute";
div.style.zIndex = "3";
div.id = "jack";
document.body.appendChild(div);

document.onmousemove=function(e){
  var x, y;
  if (e) {x=e.clientX; y=e.clientY;} 
  else {x=event.clientX;y=event.clientY;}
  var jack = document.getElementById('jack');
  jack.style.top=y+'px';
  jack.style.left=x+50+'px';
};

Answer 2

同样的故事： getElement s ByClassName（）返回HTMLCollection（HTMLElements数组），getElement s ByClassName（＆＃34; css-class＆＃34;）[0]是找到的第一个HTMLElement

唯一的例外是getElementById（）方法。它返回单个HTMLElement（因为id属性是唯一的 - 一个文档不能包含两个具有相同id值的元素）

Div仍为零读数

2 个答案: