Promise封装Ajax，让网络请求的异步操作变得更简单
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<script>
//XHR对象
const getJSON=function(url){
const promise=new Promise(function(resolve,reject){
//异步操作：网络请求代码
const handler=function(){
if(this.readyState!==4){
// 0 1 2 3 4
return;
}
if(this.status===200){
resolve(this.response)
}else{
reject(new Error(this.statusText))
}
}
const client=new XMLHttpRequest();
client.open("GET",url);
client.onreadystatechange=handler;
client.responseType="json";
client.setRequestHeader("Accept","application/json");
client.send();
})
return promise;
}
getJSON("http://........")//网络请求的地址，接口
.then(function(data){
console.log(data);
},function(error){
console.log(error);
})
</script>
</body>
</html>
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