jsonp原理.html

<!DOCTYPE html>
<html lang="en">

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

<body>

</body>
<script>
    function jsonp(url, data) {
        return new Promise((resolve, reject) => {
            // 1.将传入的data数据转化为url字符串形式
            var queryString = url.indexOf("?") == -1 ? "?" : "&";
            var arr = []
            for (var key in data) {
                arr.push(key + "=" + encodeURIComponent(data[key]))
            }
            queryString += arr.join("&");
            // 2.处理url中的回调函数
            var callbackName =
                "jsonp_callback_" +
                Math.random()
                    .toString(16)
                    .replace(".", "");
            queryString += "&callback=" + callbackName;

            // 3.创建一个script标签并插入到页面中
            var script = document.createElement("script");
            script.src = url + queryString;

            // 4.挂载回调函数
            window[callbackName] = function (data) {
                resolve(data);
                // 处理完回调函数的数据之后，删除jsonp的script标签
                document.body.removeChild(script);
            };

            document.body.appendChild(script);
        });
    }

    jsonp('http://127.0.0.1:3000/show', { name: '测试', age: 20 }).then((res) => {
        console.log(res)
    }).catch((err) => {
        console.log('xx===')
        console.log(err)
    })
</script>

</html>