通过javascript

Question

这些代码不起作用。

var x = document.getElementsByClassName("circle");
for (var i = 0; i < x.length; i++) {
    x[i].onclick = function(){ alert("hello!");};
}

Answer 1

＆＃13;

＆＃13;

var x = document.getElementsByClassName("circle");
for (var i = 0; i < x.length; i++) {
  x[i].onclick = function() {
    this.style.opacity = 0
  };
}

＆＃13;

.circle {
  width: 100px;
  height: 100px;
  background: red;
  border-radius: 50%;
  margin: 20px;
  float: left;
  transition: all .3s linear;
}

＆＃13;

<div class="circle"></div>
<div class="circle"></div>
<div class="circle"></div>
<div class="circle"></div>

＆＃13;

＆＃13;

＆＃13;

Answer 2

这样做更好：

for ( i = 0; i < x; i++) {
   x[i].addEventListener('click', function() { alert('Hello World') });
}