文件上传：<input type="file" /> （IE9及以下不支持下面这些功能，其它浏览器最新版本均已支持。）
1、允许上传文件数量
允许选择多个文件：<input type="file" multiple>只允许上传一个文件：<input ?type="file" single>
2、上传指定的文件格式
<input type="file" accept="image/gif,image/png" />
这里的上传格式仅指打开上传弹窗选择文件时默认的文件格式，可手动修改成其它文件格式。
如果不限制上传图片的格式可写成：accept="image/*"
其它格式参考如下：
*.3gpp ??audio/3gpp, video/3gpp ???3GPP Audio/Video*.ac3 ???audio/ac3 ???AC3 Audio*.asf ???allpication/vnd.ms-asf ???Advanced Streaming Format*.au ????audio/basic ???AU Audio*.css ???text/css ???Cascading Style Sheets*.csv ???text/csv ???Comma Separated Values*.doc ???application/msword ???MS Word Document*.dot ???application/msword ???MS Word Template*.dtd ???application/xml-dtd ???Document Type Definition*.dwg ???image/vnd.dwg ???AutoCAD Drawing Database*.dxf ???image/vnd.dxf ???AutoCAD Drawing Interchange Format*.gif ???image/gif ???Graphic Interchange Format*.htm ???text/html ???HyperText Markup Language*.html ??text/html ???HyperText Markup Language*.jp2 ???image/jp2 ???JPEG-2000*.jpe ???image/jpeg ???JPEG*.jpeg ??image/jpeg ???JPEG*.jpg ???image/jpeg ???JPEG*.js ????text/javascript, application/javascript ???JavaScript*.json ??application/json ???JavaScript Object Notation*.mp2 ???audio/mpeg, video/mpeg ???MPEG Audio/Video Stream, Layer II*.mp3 ???audio/mpeg ???MPEG Audio Stream, Layer III*.mp4 ???audio/mp4, video/mp4 ???MPEG-4 Audio/Video*.mpeg ??video/mpeg ???MPEG Video Stream, Layer II*.mpg ???video/mpeg ???MPEG Video Stream, Layer II*.mpp ???application/vnd.ms-project ???MS Project Project*.ogg ???application/ogg, audio/ogg ???Ogg Vorbis*.pdf ???application/pdf ???Portable Document Format*.png ???image/png ???Portable Network Graphics*.pot ???application/vnd.ms-powerpoint ???MS PowerPoint Template*.pps ???application/vnd.ms-powerpoint ???MS PowerPoint Slideshow*.ppt ???application/vnd.ms-powerpoint ???MS PowerPoint Presentation*.rtf ???application/rtf, text/rtf ???Rich Text Format*.svf ???image/vnd.svf ???Simple Vector Format*.tif ???image/tiff ???Tagged Image Format File*.tiff ??image/tiff ???Tagged Image Format File*.txt ???text/plain ???Plain Text*.wdb ???application/vnd.ms-works ???MS Works Database*.wps ???application/vnd.ms-works ???Works Text Document*.xhtml ?application/xhtml+xml ???Extensible HyperText Markup Language*.xlc ???application/vnd.ms-excel ???MS Excel Chart*.xlm ???application/vnd.ms-excel ???MS Excel Macro*.xls ???application/vnd.ms-excel ???MS Excel Spreadsheet*.xlt ???application/vnd.ms-excel ???MS Excel Template*.xlw ???application/vnd.ms-excel ???MS Excel Workspace*.xml ???text/xml, application/xml ???Extensible Markup Language*.zip ???aplication/zip ???Compressed Archive
3、FileList上传文件数组
FileList对象都是一组文件对象的集合，而文件对象则拥有下列的属性：
name – 文件名（不包含路径）
type – 文件的MIME类型（小写）
size – 文件的尺寸（单位为字节）
lastModifiedDate 为上传文件的最后修改时间
通过上面的几个对象，我们能够控制用户上传的文件大小和文件类型，以便减轻服务器再次检测时的压力，并提升安全系数
var a=document.getElementById("file");a.onchange=function(e){e=e || window.event;var b=e.target.files;alert(b[0].name);}4、拖动上传
dataTransfer 对象
dropEffect[=sCursorStyle]
设置或获取拖拽操作的类型和要显示的光标类型
copy：复制样式被显示
link：链接样式被显示
move：移动样式被显示
none：默认,没有鼠标样式被定义
effectAllowed[=sEffect]
设置或获取数据传送操作可应用与该对象的源元素
copy 选项被复制
link 选项被dataTransfer作为link方式保存
move 当放置时,对象被移动至目标对象
copylink 选项是被复制还是被作为link方式保存关键在于目标对象
linkmove 选项是被作为link方式保存还是被移动关键在于目标对象
all 所有效果都被支持
none 不支持任何效果
uninitialized 默认不能通过这个属性传递任何值
setData(sFormat,sData) 将指定格式的数据赋值给dataTransfer或者clipboardData sFormat:URL,Text
getData(sFormat) 从dataTransfer或者clipboardData中获取值 sFormat:URL,Text
clearData([sFormat]) 通过dataTransfer或者clipboardData中删除某种格式的数据 sFormat:Text,URL,File,HTML,Image
<!DOCTYPE HTML> <html> <head> <meta charset="utf-8"> <title></title> <style type="text/css">#DropZone{border:1px solid #CCC;height:50px;}</style></head><body><input type="file" multiple accept="image/gif,image/png" id="file"><div id="DropZone"></div><div id="Lists"></div><script>var aa=document.getElementById("file");aa.onchange=function(){fileDrop();} function fileDrop(e) { ???e = e || window.event; ????????e.stopPropagation(); // 阻止冒泡 ???e.preventDefault(); ?//阻止默认行为 ????????var files = e.dataTransfer.files; ??//FileList ????????var output = []; ????????for(var i = 0, f; f = files[i]; i++) { ???????output.push(‘<li><strong>‘ + f.name + ‘</strong>(‘ + f.type + ‘) - ‘ + f.size +‘ bytes</li>‘); ???} ????????document.getElementById(‘Lists‘).innerHTML = ‘<ul>‘ + output.join(‘‘) + ‘</ul>‘;}; function dragOver(e) { ???e = e || window.event; ????????e.stopPropagation(); ???e.preventDefault(); ???e.dataTransfer.dropEffect = ‘copy‘; //指定拖放视觉效果};var d = document.getElementById(‘DropZone‘); try { ???d.addEventListener(‘dragover‘, dragOver, false); ???d.addEventListener(‘drop‘, fileDrop, false)} catch(ex) { ???document.write(‘something must be wrong!‘);} </script></body></html>5、FileReader文件预览，读取文件数据（同时可读取图片文件宽高）
FileReader包含四种异步读取文件的方式：
FileReader.readAsBinaryString(Blob|File) - result属性包含的是file/blob的二进制字符串形式的数据。每个字节由一个0-255的整数表示。
FileReader.readAsText(Blob|File, opt_encoding) - result属性包含的是以文本方式表示的file/blob数据。默认情况下，字符串以‘UTF-8‘编码方式解码。使用opt_encoding参数可以指定一个不同的格式。
FileReader.readAsDataURL(Blob|File) - result属性包含的是以data URL编码的file/blob数据。
FileReader.readAsArrayBuffer(Blob|File) - result属性包含的是以ArrayBuffer对象表示的file/blob数据。
一旦这些read方法被调用，onloadstart, onprogress, onload, onabort, onerror, onloadend就可以被用来追踪进度。
<!DOCTYPE HTML> <html> <head> <meta charset="utf-8"> <title></title> <style type="text/css">body{margin:0;padding:0;}img{vertical-align:bottom;}</style></head><body><input type="file" multiple accept="image/gif,image/png,,image/jpeg" id="Files"><div id="Preview"></div><ul id="Errors"></ul><script>function fileSelect(e) { ???e = e || window.event; ????????var files = e.target.files; ?//FileList Objects ???????var ireg = /image\/.*/i, ???????p = document.getElementById(‘Preview‘); ????????????var ul = document.getElementById(‘Errors‘); ???for(var i = 0, f; f = files[i]; i++) { ???????if(!f.type.match(ireg)) { ???????????//设置错误信息 ???????????var li = document.createElement(‘li‘); ???????????li.innerHTML = ‘<li>‘ + f.name +‘不是图片文件.</li>‘; ????????????????????????ul.appendChild(li); ????????????????????????continue; ???????} ????????????????var reader = new FileReader(); ????????????????reader.onload = (function(file) { ???????????return function(e) { ???????????????var span = document.createElement(‘span‘);var img = new Image;img.alt=file.name;img.onload = function() {console.log(img.height); // image is loaded; sizes are available}; img.src=this.result; ???????????????span.innerHTML = ‘<img class="thumb" src="‘+ this.result +‘" alt="‘+ file.name +‘" />‘; ????????????????????????????????p.insertBefore(span, null); ???????????}; ???????})(f); ???????//读取文件内容 ???????reader.readAsDataURL(f); ???}} ????if(window.File && window.FileList && window.FileReader && window.Blob) { ???document.getElementById(‘Files‘).addEventListener(‘change‘, fileSelect, false);} else { ???document.write(‘您的浏览器不支持File Api‘);}</script></body></html>上传txt文件内容预览(需对<>&‘"|等符号进行过滤否则会中断读取)：
<!DOCTYPE HTML> <html> <head> <meta charset="utf-8"> <title></title> <style type="text/css">body{margin:0;padding:0;}img{vertical-align:bottom;}</style></head><body><input type="file" multiple id="Files"><div id="Preview"></div><ul id="Errors"></ul><script>function encodeHTML(source) { ?//return source; ???return source ?????????????.replace(/&/g, ‘&‘) ?????????????.replace(/</g, ‘<‘) ?????????????.replace(/>/g, ‘>‘) ???????????.replace(/\"/g, ‘"‘);}; ?function fileSelect(e) { ?????e = e || window.event; ????????????var files = e.target.files; ?//FileList Objects ?????????var ireg = /text\/.*/i, ?????????p = document.getElementById(‘Preview‘); ????????????????var ul = document.getElementById(‘Errors‘); ?????for(var i = 0, f; f = files[i]; i++) { ?????????console.log(f.type); ?????????if(!f.type.match(ireg)) { ?????????????//设置错误信息 ?????????????var li = document.createElement(‘li‘); ?????????????li.innerHTML = ‘<li>‘ + f.name +‘不是文本文件.</li>‘; ????????????????????????????ul.appendChild(li); ????????????????????????????continue; ?????????} ????????????????????var reader = new FileReader(); ????????????????????reader.onload = (function(file) { ?????????????return function(e) { ?????????????????var div = document.createElement(‘div‘); ?????????????????div.className = "text" ?????????????????div.innerHTML = encodeHTML(this.result); ????????????????????????????????????p.insertBefore(div, null); ?????????????}; ?????????})(f); ?????????//读取文件内容 ?????????reader.readAsText(f); ?????} ?} ????????if(window.File && window.FileList && window.FileReader && window.Blob) { ?????document.getElementById(‘Files‘).addEventListener(‘change‘, fileSelect, false); ?} else { ?????document.write(‘您的浏览器不支持File Api‘); ?} ?</script></body></html>读取上传txt指定区域文本内容：
<!DOCTYPE HTML> <html> <head> <meta charset="utf-8"> <title></title> <style type="text/css">body{margin:0;padding:0;}img{vertical-align:bottom;}</style></head><body><input type="file" multiple id="Files"><button type="button" id="buttons" data-start="0" data-end="3">确定</button><div id="range"></div><div id="content"></div><script> function readBlob(start, end) { ?????var files = document.getElementById(‘Files‘).files; ????????????if(!files.length) { ?????????alert(‘请选择文件‘); ?????????return false; ?????} ????????????var file = files[0], ?????????start = parseInt(start, 10) || 0, ?????????end = parseInt(end, 10) || (file.size - 1); ????????????????var r = document.getElementById(‘range‘), ?????????c = document.getElementById(‘content‘); ????????????????var reader = new FileReader(); ??????reader.onloadend = function(e) { ?????????if(this.readyState == FileReader.DONE) { ?????????????c.textContent = this.result; ?????????????r.textContent = "Read bytes: " + (start + 1) + " - " + (end + 1) + " of " + file.size + " bytes"; ?????????} ?????}; ??????var blob; ?????????????blob = file.slice(start, end + 1, ‘text/plain;charset=UTF-8‘); ?????reader.readAsBinaryString(blob); ?}; ????try { ?????document.getElementById(‘buttons‘).addEventListener(‘click‘, function(e) { ?????????if(e.target.tagName.toLowerCase() == ‘button‘) { ?????????????var start = e.target.getAttribute(‘data-start‘), ?????????????????end = e.target.getAttribute(‘data-end‘); ????????????????????????????????readBlob(start, end); ?????????} ???????}); ?} catch(ex) { ?????alert(‘something error happens!‘) ?} ?</script></body></html>File接口提供了slice方法支持把文件切成不同的片段,第一个参数是起始的字节数,第二个参数是结束的字节数，还有一个可选的内容类型字符串可以作为第三个参数。早期的chrome和firefox版本不支持file.slice 可使用file.webkitSlice和file.mozSlice替代，最新版本均支持file.slice。
6、文件读取进度
<!DOCTYPE HTML> <html> <head> <meta charset="utf-8"> <title></title> </head><body><form> ?????<fieldset> ?????????<legend>分度读取文件：</legend> ?????????<input type="file" id="File" /> ?????????<input type="button" value="中断" id="Abort" /> ?????????<p> ?????????????<label>读取进度：</label><progress id="Progress" value="0" max="100"></progress> ?????????</p> ?????????<p id="Status"></p> ?????</fieldset> ?</form> ??<script>var h = { ?????init: function() { ?????????var me = this; ????????????????????document.getElementById(‘File‘).onchange = me.fileHandler; ?????????document.getElementById(‘Abort‘).onclick = me.abortHandler; ????????????????????me.status = document.getElementById(‘Status‘); ?????????me.progress = document.getElementById(‘Progress‘); ?????????me.percent = document.getElementById(‘Percent‘); ????????????????????me.loaded = 0; ?????????//每次读取1M ?????????me.step = 1024 * 1024; ?????????me.times = 0; ?????}, ?????fileHandler: function(e) { ?????????var me = h; ????????????????????var file = me.file = this.files[0]; ?????????var reader = me.reader = new FileReader(); ????????????????????// ?????????me.total = file.size; ????????????????????reader.onloadstart = me.onLoadStart; ?????????reader.onprogress = me.onProgress; ?????????reader.onabort = me.onAbort; ?????????reader.onerror = me.onerror; ?????????reader.onload = me.onLoad; ?????????reader.onloadend = me.onLoadEnd; ?????????//读取第一块 ?????????me.readBlob(file, 0); ???}, ?????onLoadStart: function() { ?????????var me = h; ?????}, ?????onProgress: function(e) { ?????????var me = h; ????????????????????me.loaded += e.loaded; ?????????//更新进度条 ?????????me.progress.value = (me.loaded / me.total) * 100; ?????}, ?????onAbort: function() { ?????????var me = h; ?????}, ?????onError: function() { ?????????var me = h; ????????????????}, ?????onLoad: function() { ?????????var me = h; ????????????if(me.loaded < me.total) { ?????????????me.readBlob(me.loaded); ?????????} else { ?????????????me.loaded = me.total; ?????????} ?????}, ?????onLoadEnd: function() { ?????????var me = h; ????????????????}, ?????readBlob: function(start) { ?????????var me = h; ????????????????????var blob, ?????????????file = me.file; ????????????????????me.times += 1; ????????????????????if(file.slice) { ?????????????blob = file.slice(start, start + me.step + 1); ?????????} else if(file.mozSlice) { ?????????????blob = file.mozSlice(start, start + me.step + 1); ?????????} ????????????????????me.reader.readAsText(blob); ?????}, ?????abortHandler: function() { ?????????var me = h; ????????????????????if(me.reader) { ?????????????me.reader.abort(); ?????????} ?????} ?}; ????h.init(); ?</script></body></html>本文代码以chrome测试为主。
参考资料：
http://blog.csdn.net/zhu1988renhui/article/details/7936498
http://blog.csdn.net/zhu1988renhui/article/details/7936525
http://dev.w3.org/2006/webapi/FileAPI/#dfn-filereader
http://www.html5rocks.com/zh/tutorials/file/dndfiles/
http://www.w3.org/TR/file-upload/
http://www.w3.org/TR/file-upload/#dfn-filereader
http://www.w3.org/TR/file-upload/#dfn-Blob
http://www.w3.org/TR/file-upload/#dfn-fileerror
http://www.w3.org/TR/progress-events/#Progress
http://www.zhangxinxu.com/wordpress/?p=1923
http://www.tfan.org/wp-content/slides/file.html#1
文件上传常见问题整理
原文地址：https://www.cnblogs.com/chenyablog/p/9957009.html