服务端php添加了sleep延迟5秒执行
服务端代码demo.php
<?php sleep(5); $name=$_POST; var_dump($name); ?>
同步请求
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>ajax</title>
</head>
<body>
<button id=button>发送请求</button>
<div id="container">
</div>
</body>
<script>
//获取按钮
var button = document.getElementById('button');
var container = document.getElementById('container');
button.onclick=function(){
//创建xmlhttpRequest请求
var xhr = new XMLHttpRequest();
//准备发送请求方式
xhr.open('POST','demo.php',false);
//发送请求
//编码转换
xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
xhr.send('name=jiub&age=12');
//接受并处理请求返回的数据
var response = xhr.responseText;
console.log(response);
container.innerHTML=response;
alert('执行完毕');
}
</script>
</html>
点击发送请求,ajax会等待服务端响应完毕才会弹出alert,这样很影响用户体验,影响js dom
异步请求
点击发送请求,服务端无响应,前端js正常执行,服务端响应成功后反回数据
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>ajax</title>
</head>
<body>
<button id=button>发送请求</button>
<div id="container">
</div>
</body>
<script>
//获取按钮
var button = document.getElementById('button');
var container = document.getElementById('container');
button.onclick=function(){
//创建xmlhttpRequest请求
var xhr = new XMLHttpRequest();
//异步请求方式
xhr.onreadystatechange = function(){
if(xhr.readyState == 4 && xhr.status == 200){
var response = xhr.responseText;
container.innerHTML=response;
}
}
//准备发送请求方式
xhr.open('POST','demo.php',true);
//发送请求
//编码转换
xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
xhr.send('name=jiub&age=12');
//接受并处理请求返回的数据
// var response = xhr.responseText;
// console.log(response);
// container.innerHTML=response;
alert('执行完毕');
}
</script>
</html>
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