发送多次ajax请求：
代码演示：
<!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>
//基于Promise发送Ajax请求
function queryData(url) {
var p = new Promise(function(resolve, reject) {
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (xhr.readyState != 4) return;
if (xhr.readyState == 4 && xhr.status == 200) {
//处理正常请况
resolve(xhr.responseText);
} else {
//处理异常情况
reject('服务器错误');
}
};
xhr.open('get', url);
xhr.send(null);
});
return p;
}
// queryData('http://localhost:3000/data')
// .then(function(data) {
// console.log(data);
// }, function(info) {
// console.log(info);
// })
//=======================================
//发送多个ajax请求并且保证顺序
queryData('http://localhost:3000/data')
.then(function(data) {
console.log(data);
return queryData('http://localhost:3000/data1')
})
.then(function(data) {
console.log(data);
return queryData('http://localhost:3000/data2')
})
.then(function(data) {
console.log(data);
})
</script>
</body>
</html>
