实例
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>js三种引入方式</title>
</head>
<body>
<!-- 直接在元素的事件方法属性上写js -->
<h3 id="测试" onclick="alert(id)">js很有趣</h3>
<form action="">
<input type="text" name="site" value="表单测试">
<button type="button" onclick="alert(site.value)">点我</button>
</form>
<hr>
<!-- js脚本直接写在script标签中，仅限当前页面 -->
<form action="">
<input type="text" name="username" placeholder="用户名">
<button type="button" onclick="check(username)">验证</button>
</form>
<script>
function check(username) {
if(username.value.length===0){
alert('空用户名');
} else{
alert('验证通过');
}
}
</script>
<hr>
<!-- 引入外部js文件 -->
<form action="">
<input type="text" name="us" placeholder="用户">
<button type="button" onclick="check(us)">测试</button>
</form>
<script src="js.js"></script>
<hr><hr>
<!-- 案例 -->
<div id="qiu"></div>
<style>
#qiu {
width: 80px;
height: 80px;
background-color: brown;
border-radius: 50%;
box-shadow: 3px 3px 3px lightblue;
position: relative;
}
</style>
<script>
var qiu=document.getElementById('qiu');
function running(){
var count=0;
var timer=setInterval(
function (){
if(count <100) {
qiu.style.left=qiu.style.top=count+'px';
count++;
} else {
clearInterval(timer);
}
}, 100);
}
qiu.addEventListener('click',running,false);
</script>
</body>
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