FileReaderreadAsArrayBufferreadAsTextreadAsDataURL
<input type=\"file\" />
Blob/File
onchange获取
对象作为参数传入
base64
readAsDataURL
readAsArrayBuffer
ArrayBuffer
text字符串
【解码】window.atobInt8ArrayString.prototype.charCodeAt
URL.createObjectURL(blob/file)生成blob协议地址
readAsText
