在做文件系统时，上传下载需要获取到文件的md5。
上传获取文件md5优点：将文件md5传至后段服务器，若服务器已存在该文件，则将该文件关联，实现‘秒传’的功能。
下载获取文件md5优点：下载文件完成后将文件md5传给后端，后端判断文件下载是否完整。
##js-spark-md5类库实现快速获取文件md5
demo如下：
<!DOCTYPE html><html lang="en"><head> ???<meta charset="UTF-8"> ???<title></title></head><body><form method="POST" enctype="multipart/form-data" onsubmit="return false;" > ???<input id=file type=file placeholder="select a file" /></form><pre id=log></pre><script src="//cdn.rawgit.com/satazor/SparkMD5/master/spark-md5.min.js"></script><script> ???var log=document.getElementById("log"); ???document.getElementById("file").addEventListener("change", function() { ???????var blobSlice = File.prototype.slice || File.prototype.mozSlice || File.prototype.webkitSlice, ???????????????file = this.files[0], ???????????????chunkSize = 2097152, // read in chunks of 2MB ???????????????chunks = Math.ceil(file.size / chunkSize), ???????????????currentChunk = 0, ???????????????spark = new SparkMD5.ArrayBuffer(), ???????????????frOnload = function(e){ ?????????????????// ?log.innerHTML+="\nread chunk number "+parseInt(currentChunk+1)+" of "+chunks; ???????????????????spark.append(e.target.result); // append array buffer ???????????????????currentChunk++; ???????????????????if (currentChunk < chunks) ???????????????????????loadNext(); ???????????????????else ???????????????????????log.innerHTML+="\n加载结束,文件md5:\n"+spark.end(); ???????????????}, ???????????????frOnerror = function () { ???????????????????log.innerHTML+="err"; ???????????????}; ???????function loadNext() { ???????????var fileReader = new FileReader(); ???????????fileReader.onload = frOnload; ???????????fileReader.onerror = frOnerror; ???????????var start = currentChunk * chunkSize, ???????????????????end = ((start + chunkSize) >= file.size) ? file.size : start + chunkSize; ???????????fileReader.readAsArrayBuffer(blobSlice.call(file, start, end)); ???????}; ???????loadNext(); ???});</script></body></html>js库在我百度网盘
链接: https://pan.baidu.com/s/1jIaJZrK 密码: yfbp
js获取文件md5库
原文地址：http://www.cnblogs.com/nanguabushuohua/p/7568270.html