> 通过base64 获取文件头判断文件类型并不准确，如果想要获取文件真实类型，需要获取文件二进制头，每种格式都有特有的二进制头。所以需要前端读取文件流，比较文件头，判断文件真实格式。 ``` function stringToBytes(string) { return [...string].map((character) => character.charCodeAt(0)) } function readBuffer(file, start = 0, end = 2) { return new Promise((resolve, reject) => { const reader = new FileReader() reader.onload = () => { resolve(reader.result) } reader.onerror = reject reader.readAsArrayBuffer(file.slice(start, end)) }) } function check(headers) { return (buffers, options = { offset: 0 }) => headers.every((header, index) => header === buffers[options.offset + index]) } const isPDF = check(stringToBytes('%PDF')) const isPNG = check([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]) export const checkFileType = async (file, accept = '*') => { const buffers = await readBuffer(file, 0, 8) const uint8Array = new Uint8Array(buffers) const acceptList = accept.split(',') for (let i = 0, length = acceptList.length; i < length; i++) { if (acceptList[i] === 'pdf' && isPDF(uint8Array)) return true else if (acceptList[i] === 'png' && isPNG(uint8Array)) return true } return Promise.reject() } ```