文件处理
1、base64转file对象let imageBase64
let blob = dataURLtoBlob(imageBase64)
let file = blobToFile(blob, Date.now() + '.png')
dataURLtoBlob(dataurl) {
var arr = dataurl.split(','),
mime = arr[0].match(/:(.*?);/)[1],
bstr = atob(arr[1]),
...