ES6解决跨域

实现一个jsonp函数，仅需要支持jsonp(url)一种调用方式即可（仅有url一个传参），例如： jsonp('//t.alicdn.com/t/gettime?callback=cb').then(result=>console.dir(result))

//需使用promise
function jsonp(url) {
//在这里书写代码
    return new Promise((resolve, reject) => {
        let callbackName = `${url.split("?")[1].split("=")[1]}${Date.now()}`
        url = url.split("?")[0] + `?${url.split("?")[1]}${Date.now()}`
        let script = document.createElement('script')
        script.src = url
        window[callbackName] = (res) => {
            delete window[callbackName]
            document.body.removeChild(script)
            if (res) {
                resolve(res)
            } else {
                reject('没有返回数据')
            }
        }
        script.addEventListener('error', () => {
            delete window[callbackName]
            document.body.removeChild(script)
            reject('script资源加载失败')
        }, false)
        document.getElementsByTagName("body")[0].appendChild(script)
    })
}
//调用
jsonp('//t.alicdn.com/t/gettime?callback=cb').then(result=>console.dir(result))