javascript可以把base64编码转换成二进制代码吗？求示例代码！

function convertBase64UrlToBytes(base64Str) {
var bytes = window.atob(urlData.split(',')[1]);
//处理异常,将ascii码小于0的转换为大于0
var ab = new ArrayBuffer(bytes.length);
var ia = new Uint8Array(ab);
for (var i = 0; i < bytes.length; i++) {
ia[i] = bytes.charCodeAt(i);
}
return ia;
}

找到一个人的转换方法,如下:
function dataURLtoBlob(dataurl) {
var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],
bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
while(n--){
u8arr[n] = bstr.charCodeAt(n);
}
return new Blob([u8arr], {type:mime});
}

function base64to2(arraybuffer) {

    var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
        
    // lookup("B") = 1
    var lookup = new Uint8Array(256);
    for (var i = 0; i < chars.length; i++) {
     lookup[chars.charCodeAt(i)] = i;
    }


    var bufferLength = base64.length * 0.75,
    len = base64.length, i, p = 0,
    encoded1, encoded2, encoded3, encoded4;
    
    if (base64[base64.length - 1] === "=") {
        bufferLength--;
        if (base64[base64.length - 2] === "=") {
            bufferLength--;
        }
    }
    
    var arraybuffer = new ArrayBuffer(bufferLength),
    bytes = new Uint8Array(arraybuffer);
    
    for (i = 0; i < len; i+=4) {
    encoded1 = lookup[base64.charCodeAt(i)];
    encoded2 = lookup[base64.charCodeAt(i+1)];
    encoded3 = lookup[base64.charCodeAt(i+2)];
    encoded4 = lookup[base64.charCodeAt(i+3)];
    
    bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
    bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
    bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
    }
    
    return arraybuffer;
}

https://github.com/danguer/blog-examples/blob/master/js/base64-binary.js