customPromise/async和await.html at master · DantinZhang/customPromise · GitHub

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<!DOCTYPE html>
<html lang="en">
<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>async/await</title>
</head>
<body>
    <script>
        const main = async () => {
            //1.非Promise则返回一个成功的Promise,值为返回值
            // return 521;
            //2.Promise则返回结果由它来决定
            return new Promise((resolve, reject) => {
                resolve('ok');
            })
            //3.抛出错误则返回错误的Promise，值为抛出的值
            // throw '错误';
        }
        console.log(main());

        async function dj() {
            const p = new Promise((resolve, reject) => {
                reject('错误嗷嗷');
            })
            try{
                const res = await p;
                console.log(res);
            }catch(e) {
                console.log(e);
            }
        }
        dj();

        //async-await发送ajax请求
        function sendAjax() {
            return new Promise((resolve, reject) => {
                const xhr = new XMLHttpRequest();
                xhr.responseType = 'json';  //指定返回结果格式
                xhr.open('GET', 'https://ku.qingnian8.com/dataApi/news/navlist.php');
                xhr.send();
                xhr.onreadystatechange = () => {
                    if (xhr.readyState === 4) {
                        if (xhr.status >= 200 && xhr.status < 300) {
                            resolve(xhr.response);
                        } else {
                            reject(xhr.status);
                        }
                    }
                }
            });
        }
        async function getNews() {
            try{
                let result = await sendAjax();
                console.log(result);
            }catch(e) {
                console.log(e);
            }
        }
        getNews();
    </script>
</body>
</html>