ailed to execute ‘readAsDataURL‘ on ‘FileReader‘: The object is already busy reading Blobs.

failed to execute ‘readAsDataURL’ on ‘FileReader’: The object is already busy reading Blobs.

注意：在遍历时把 var fileReader = new FileReader(); 放到了循环之外,
会导致了failed to execute ‘readAsDataURL’ on ‘FileReader’: The object is already busy reading Blobs.错误，
这个FileReader应该对应于每一个读取的文件都需要重新new一个。

	_files.forEach(file=>{
    
    
			const fr = new FileReader()
			fr.readAsDataURL(file)
			fr.onload = e=>{
    
    
				let base=e.target.result
				spark.append(base)
				base64 = spark.end().slice(0,5)
				suffix=/\.(a-zA-Z0-9)+$/.exec(file.name)
				file.name=`${
      
      base64}-${
      
      suffix}`
			}
		})