SOURCE

function jsonp({ url, params, callback }) {
    return new Promise((resolve, reject) => {
        // 创建临时的scipt 标签，用于发起请求
        const script = document.createElement('script')
        // 绑定callback到window上，执行完回调函数后，移除script标签
        window[callback] = data => {
            resolve(data)
            document.removeChild(script)
        }

        // 构造 GET 请求参数，key=value&callback=callback
        const formatParams = { ...params, callback };
        const requestParams = Object.keys(formatParams)
            .reduce((acc, cur) => {
                return acc.concat([`${cur}=${formatParams[cur]}`]);
            }, [])
            .join('&');
        // 构造 GET 请求的 url 地址
        const src = `${url}?${requestParams}`;
        script.setAttribute('src', src);
        document.body.appendChild(script);

    })
}

// 调用时
jsonp({
  url: 'https://xxx.xxx',
  params: {id:2},
  callback: 'fn',
})

//<script src='https://xxx.xxx.xx?id=2&callback=fn'><script>