JavaScript文件上传的常见问题整理

来源：jb51　　时间：2022/6/27 16:57:46　　对本文有异议

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>