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老师批语：
在实际开发中，我们经常需要将页面元素进行运动和拖拽以获取更好的页面效果
1、运动原理：即改变盒子的offsetLeft属性来获得位置的改变，取得一个盒子的运动效果
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>js运动原理</title>
<style>
.ball1{
width: 100px;
height: 100px;
background-color: aquamarine;
border-radius: 50%;
position: absolute;
top:50px;
left:50px;
}
</style>
</head>
<body>
<button>动起来</button>
<button onclick="reset()">复位</button>
<div class="ball1"></div>
<script>
var btn = document.querySelector('button');
var ball1 = document.getElementsByClassName('ball1')[0];
var timer = null;
btn.onclick = function(){
clearInterval(timer);
timer = setInterval(function() {
if(ball1.offsetLeft < 500){
ball1.style.left = ball1.offsetLeft+5+'px';
}else{
clearInterval(timer);
}
},100);
}
function reset() {
clearInterval(timer);
ball1.style.left = '50px';
}
</script>
</body>
</html>点击 "运行实例" 按钮查看在线实例
2、拖拽原理：分三个动作，选中 移动 放下
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>拖拽</title>
<style>
.ball2{
width: 100px;
height: 100px;
background-color: aquamarine;
border-radius: 50%;
position: absolute;
top:100px;
left:100px;
}
</style>
</head>
<body>
<div class="ball2"></div>
</body>
<script>
//onmousedown 选中 onmousemove 移动 onmouseup 放下
var ball2 = document.getElementsByClassName('ball2')[0];
//event.clientX 鼠标横轴 event.clientY鼠标纵轴
ball2.onmousedown = function (event) {
var x = event.clientX - ball2.offsetLeft;
var y = event.clientY - ball2.offsetTop;
document.onmousemove = function(event) {
ball2.style.left = event.clientX - x +'px';
ball2.style.top = event.clientY - y +'px';
}
document.onmouseup = function() {
document.onmousemove = null;
}
}
</script>
</html>点击 "运行实例" 按钮查看在线实例
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