base64编码文件下载

比方说，我有一个bse64如下的编码文件：

const base64Str = 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然后封装的下载方法

function downloadByBase64(base64Str, fileName) {
    const fileNameGroup = fileName.split('.');
    const fileType = fileNameGroup[fileNameGroup.length - 1]
    const typeDic = {
    'docx': 'application/msword',
    'doc': 'application/msword',
    'bin': 'application/octet-stream',
    'exe': 'application/octet-stream',
    'so': 'application/octet-stream',
    'dll': 'application/octet-stream',
    'pdf': 'application/pdf',
    'ai': 'application/postscript',
    'xls': 'application/vnd.ms-excel',
    'ppt': 'application/vnd.ms-powerpoint',
    'dir': 'application/x-director',
    'js': 'application/x-javascript',
    'swf': 'application/x-shockwave-flash',
    'xhtml': 'application/xhtml+xml',
    'xht': 'application/xhtml+xml',
    'zip': 'application/zip',
    'mid': 'audio/midi',
    'midi': 'audio/midi',
    'mp3': 'audio/mpeg',
    'rm': 'audio/x-pn-realaudio',
    'rpm': 'audio/x-pn-realaudio-plugin',
    'wav': 'audio/x-wav',
    'bmp': 'image/bmp',
    'gif': 'image/gif',
    'jpeg': 'image/jpeg',
    'jpg': 'image/jpeg',
    'png': 'image/png',
    'css': 'text/css',
    'html': 'text/html',
    'htm': 'text/html',
    'txt': 'text/plain',
    'xsl': 'text/xml',
    'xml': 'text/xml',
    'mpeg': 'video/mpeg',
    'mpg': 'video/mpeg',
    'avi': 'video/x-msvideo',
    'movie': 'video/x-sgi-movie'
}
    // 将base64转为blob对象
    const bstr = atob(base64Str);
    console.log(bstr.length);
    let n = bstr.length;
    const u8arr = new Uint8Array(n);
    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    const fileBlob = new Blob([u8arr], { type: typeDic[fileType] });
    const downloadUrl = window.URL.createObjectURL(fileBlob);
    const anchor = document.createElement("a");
    anchor.href = downloadUrl;
    anchor.download = fileName
    anchor.click();
    window.URL.revokeObjectURL(fileBlob);
}

使用如下

<button>开始下载</button>
<script>
    document.querySelector('button').onclick=function(){
       downloadByBase64(base64Str, '杜三芳、吴学礼犯故意杀人罪二审裁定书（含死刑和死缓被告人）.docx')
    }
</script>