获取某个网址的文件内容

比如想在本地获取到https://unpkg.com/element-ui@2.15.1/lib/theme-chalk/index.css这个文件的内容

      getFile (url, isBlob = false) {
        return new Promise((resolve, reject) => {
          const client = new XMLHttpRequest()
          client.responseType = isBlob ? 'blob' : ''
          client.onreadystatechange = () => {
            if (client.readyState !== 4) {
              return
            }
            if (client.status === 200) {
              const urlArr = client.responseURL.split('/')
              resolve({
                data: client.response,
                url: urlArr[urlArr.length - 1]
              })
            } else {
              reject(new Error(client.statusText))
            }
          }
          client.open('GET', url)
          client.send()
        })
      }

      getIndexStyle () {
        this.getFile('//unpkg.com/element-ui/lib/theme-chalk/index.css')
          .then(({ data }) => {
            this.originalStyle = this.getStyleTemplate(data)
          })
      },