javascript实现限制上传文件的大小

基本思路
示例

[一]、基本思路

在FireFox、Chrome浏览器中可以根据document.getElementById(“id_file”).files[0].size 获取上传文件的大小（字节数），而IE浏览器中不支持该属性，只能借助<img>标签的dynsrc属性，来间接实现获取文件的大小（但需要同意ActiveX控件的运行）。

[二]、示例

测试代码：filesize-check.html

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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

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<html xmlns="http://www.w3.org/1999/xhtml">

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    <head>

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    <meta name="DEscription" contect="my code demo" />

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    <meta name="Author" contect="Michael@www.micmiu.com" />

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    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

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    <title>js check file size @ www.micmiu.com</title>

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    </head>

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    <body>

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        <img id="tempimg" dynsrc="" src="" style="display:none" />

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        <input type="file" name="file" id="fileuploade" size="40" />

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        <input type="button" name ="check" value="checkfilesize"onclick="checkfile()"/>

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    </body>

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    <script type="text/javascript">

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        var maxsize = 2*1024*1024;//2M

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        var errMsg = "上传的附件文件不能超过2M！！！";

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        var tipMsg = "您的浏览器暂不支持计算上传文件的大小，确保上传文件不要超过2M，建议使用IE、FireFox、Chrome浏览器。";

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        var  browserCfg = {};

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        var ua = window.navigator.userAgent;

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        if (ua.indexOf("MSIE")>=1){

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            browserCfg.ie = true;

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        }else if(ua.indexOf("Firefox")>=1){

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            browserCfg.firefox = true;

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        }else if(ua.indexOf("Chrome")>=1){

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            browserCfg.chrome = true;

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        }

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        function checkfile(){

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            try{

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                var obj_file = document.getElementById("fileuploade");

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                if(obj_file.value==""){

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                    alert("请先选择上传文件");

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                    return;

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                }

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                var filesize = 0;

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                if(browserCfg.firefox || browserCfg.chrome ){

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                    filesize = obj_file.files[0].size;

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                }else if(browserCfg.ie){

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                    var obj_img = document.getElementById('tempimg');

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                    obj_img.dynsrc=obj_file.value;

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                    filesize = obj_img.fileSize;

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                }else{

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                    alert(tipMsg);

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                return;

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                }

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                if(filesize==-1){

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                    alert(tipMsg);

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                    return;

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                }else if(filesize>maxsize){

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                    alert(errMsg);

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                    return;

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                }else{

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                    alert("文件大小符合要求");

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                    return;

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                }

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            }catch(e){

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                alert(e);

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            }

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        }

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    </script>

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</html>

测试上传的文件大小：

各浏览器中的效果如下：

IE8：

FF(11.0)：

Chrome(19.0.1084.56 m)：

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