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9、使用promise封装ajax.html

<!DOCTYPE html>
<html lang="zh-CN">

    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
    </head>

    <body>
        <script>
            // Promise封装Ajax请求
            function ajax(method,url,data) {
                var xhr=new XMLHttpRequest();
                return new Promise(function(resolve,reject) {
                    xhr.onreadystatechange=function() {
                        if(xhr.readyState!==4) return;
                        if(xhr.status===200) {
                            resolve(xhr.responseText);
                        } else {
                            reject(xhr.statusText);
                        }

                    };
                    xhr.open(method,url);
                    xhr.send(data);
                });
            }
        </script>
    </body>

</html>