此demo为大于1M对图片进行压缩上传
若小于1M则原图上传，可以根据自己实际需求更改。
demo源码如下：
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>XMLHttpRequest上传文件</title> <script type="text/javascript"> /* 三个参数 file：一个是文件(类型是图片格式)， w：一个是文件压缩的后宽度，宽度越小，字节越小 objDiv：一个是容器或者回调函数 photoCompress() */ function photoCompress(file,w,objDiv){ var ready=new FileReader(); /*开始读取指定的Blob对象或File对象中的内容. 当读取操作完成时,readyState属性的值会成为DONE,如果设置了onloadend事件处理程序,则调用之.同时,result属性中将包含一个data: URL格式的字符串以表示所读取文件的内容.*/ ready.readAsDataURL(file); ready.onload=function(){ var re=this.result; canvasDataURL(re,w,objDiv) } } function canvasDataURL(path, obj, callback){ var img = new Image(); img.src = path; img.onload = function(){ var that = this; // 默认按比例压缩 var w = that.width, h = that.height, scale = w / h; w = obj.width || w; h = obj.height || (w / scale); var quality = 0.7; // 默认图片质量为0.7 //生成canvas var canvas = document.createElement('canvas'); var ctx = canvas.getContext('2d'); // 创建属性节点 var anw = document.createAttribute("width"); anw.nodeValue = w; var anh = document.createAttribute("height"); anh.nodeValue = h; canvas.setAttributeNode(anw); canvas.setAttributeNode(anh); ctx.drawImage(that, 0, 0, w, h); // 图像质量 if(obj.quality && obj.quality <= 1 && obj.quality > 0){ quality = obj.quality; } // quality值越小，所绘制出的图像越模糊 var base64 = canvas.toDataURL('image/jpeg', quality); // 回调函数返回base64的值 callback(base64); } } /** * 将以base64的图片url数据转换为Blob * @param urlData * 用url方式表示的base64图片数据 */ function convertBase64UrlToBlob(urlData){ var arr = urlData.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}); }</span><span style="background-color: #f5f5f5; color: #0000ff">var</span><span style="background-color: #f5f5f5; color: #000000"> xhr; </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000">上传文件方法</span> <span style="background-color: #f5f5f5; color: #0000ff">function</span><span style="background-color: #f5f5f5; color: #000000"> UpladFile() { </span><span style="background-color: #f5f5f5; color: #0000ff">var</span><span style="background-color: #f5f5f5; color: #000000"> fileObj </span><span style="background-color: #f5f5f5; color: #000000">=</span><span style="background-color: #f5f5f5; color: #000000"> document.getElementById(</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">file</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">).files[</span><span style="background-color: #f5f5f5; color: #000000">0</span><span style="background-color: #f5f5f5; color: #000000">]; </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000"> js 获取文件对象</span> <span style="background-color: #f5f5f5; color: #0000ff">var</span><span style="background-color: #f5f5f5; color: #000000"> url </span><span style="background-color: #f5f5f5; color: #000000">=</span> <span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">后台图片上传接口</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">; </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000"> 接收上传文件的后台地址 </span> <span style="background-color: #f5f5f5; color: #0000ff">var</span><span style="background-color: #f5f5f5; color: #000000"> form </span><span style="background-color: #f5f5f5; color: #000000">=</span> <span style="background-color: #f5f5f5; color: #0000ff">new</span><span style="background-color: #f5f5f5; color: #000000"> FormData(); </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000"> FormData 对象</span> <span style="background-color: #f5f5f5; color: #0000ff">if</span><span style="background-color: #f5f5f5; color: #000000">(fileObj.size</span><span style="background-color: #f5f5f5; color: #000000">/</span><span style="background-color: #f5f5f5; color: #000000">1024 > 1025) { </span><span style="background-color: #f5f5f5; color: #000000">//</span><span style="background-color: #f5f5f5; color: #000000">大于1M，进行压缩上传</span>photoCompress(fileObj, {
quality: 0.2
}, function(base64Codes){
//console.log("压缩后：" + base.length / 1024 + " " + base);
var bl = convertBase64UrlToBlob(base64Codes);
form.append("file", bl, "file_"+Date.parse(new Date())+".jpg"); // 文件对象
xhr = new XMLHttpRequest(); // XMLHttpRequest 对象
xhr.open("post", url, true); //post方式，url为服务器请求地址，true 该参数规定请求是否异步处理。
xhr.onload = uploadComplete; //请求完成
xhr.onerror = uploadFailed; //请求失败
xhr.upload.onprogress = progressFunction;//【上传进度调用方法实现】
xhr.upload.onloadstart = function(){//上传开始执行方法
ot = new Date().getTime(); //设置上传开始时间
oloaded = 0;//设置上传开始时，以上传的文件大小为0
};xhr.send(form); </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000">开始上传，发送form数据</span>});
}else{ //小于等于1M 原图上传
form.append("file", fileObj); // 文件对象
xhr = new XMLHttpRequest(); // XMLHttpRequest 对象
xhr.open("post", url, true); //post方式，url为服务器请求地址，true 该参数规定请求是否异步处理。
xhr.onload = uploadComplete; //请求完成
xhr.onerror = uploadFailed; //请求失败
xhr.upload.onprogress = progressFunction;//【上传进度调用方法实现】
xhr.upload.onloadstart = function(){//上传开始执行方法
ot = new Date().getTime(); //设置上传开始时间
oloaded = 0;//设置上传开始时，以上传的文件大小为0
};xhr.send(form); </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000">开始上传，发送form数据</span>}
}progressBar.max = evt.total;</span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000">上传成功响应</span> <span style="background-color: #f5f5f5; color: #0000ff">function</span><span style="background-color: #f5f5f5; color: #000000"> uploadComplete(evt) { </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000">服务断接收完文件返回的结果</span> <span style="background-color: #f5f5f5; color: #0000ff">var</span><span style="background-color: #f5f5f5; color: #000000"> data </span><span style="background-color: #f5f5f5; color: #000000">=</span><span style="background-color: #f5f5f5; color: #000000"> JSON.parse(evt.target.responseText); </span><span style="background-color: #f5f5f5; color: #0000ff">if</span><span style="background-color: #f5f5f5; color: #000000">(data.success) { alert(</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">上传成功！</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">); }</span><span style="background-color: #f5f5f5; color: #0000ff">else</span><span style="background-color: #f5f5f5; color: #000000">{ alert(</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">上传失败！</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">); } } </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000">上传失败</span> <span style="background-color: #f5f5f5; color: #0000ff">function</span><span style="background-color: #f5f5f5; color: #000000"> uploadFailed(evt) { alert(</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">上传失败！</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">); } </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000">取消上传</span> <span style="background-color: #f5f5f5; color: #0000ff">function</span><span style="background-color: #f5f5f5; color: #000000"> cancleUploadFile(){ xhr.abort(); } </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000">上传进度实现方法，上传过程中会频繁调用该方法</span> <span style="background-color: #f5f5f5; color: #0000ff">function</span><span style="background-color: #f5f5f5; color: #000000"> progressFunction(evt) { </span><span style="background-color: #f5f5f5; color: #0000ff">var</span><span style="background-color: #f5f5f5; color: #000000"> progressBar </span><span style="background-color: #f5f5f5; color: #000000">=</span><span style="background-color: #f5f5f5; color: #000000"> document.getElementById(</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">progressBar</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">); </span><span style="background-color: #f5f5f5; color: #0000ff">var</span><span style="background-color: #f5f5f5; color: #000000"> percentageDiv </span><span style="background-color: #f5f5f5; color: #000000">=</span><span style="background-color: #f5f5f5; color: #000000"> document.getElementById(</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">percentage</span><span style="background-color: #f5f5f5; color: #000000">"</span><span style="background-color: #f5f5f5; color: #000000">); </span><span style="background-color: #f5f5f5; color: #008000">//</span><span style="background-color: #f5f5f5; color: #008000"> event.total是需要传输的总字节，event.loaded是已经传输的字节。如果event.lengthComputable不为真，则event.total等于0</span> <span style="background-color: #f5f5f5; color: #0000ff">if</span><span style="background-color: #f5f5f5; color: #000000"> (evt.lengthComputable) {</span><span style="background-color: #f5f5f5; color: #008000">//
progressBar.value = evt.loaded;
percentageDiv.innerHTML = Math.round(evt.loaded / evt.total * 100) + "%";
}
var time = document.getElementById("time");
var nt = new Date().getTime();//获取当前时间
var pertime = (nt-ot)/1000; //计算出上次调用该方法时到现在的时间差，单位为s
ot = new Date().getTime(); //重新赋值时间，用于下次计算
var perload = evt.loaded - oloaded; //计算该分段上传的文件大小，单位b
oloaded = evt.loaded;//重新赋值已上传文件大小，用以下次计算
//上传速度计算
var speed = perload/pertime;//单位b/s
var bspeed = speed;
var units = 'b/s';//单位名称
if(speed/1024>1){
speed = speed/1024;
units = 'k/s';
}
if(speed/1024>1){
speed = speed/1024;
units = 'M/s';
}
speed = speed.toFixed(1);
//剩余时间
var resttime = ((evt.total-evt.loaded)/bspeed).toFixed(1);
time.innerHTML = '，速度：'+speed+units+'，剩余时间：'+resttime+'s';
if(bspeed==0) time.innerHTML = '上传已取消';
}
</script>
</head>
<body>
<progress id="progressBar" value="0" max="100" style=" 300px;"></progress>
<span id="percentage"></span><span id="time"></span>
<br /><br />
<input type="file" id="file" name="myfile"accept="image/x-png, image/jpg, image/jpeg, image/gif"/>
<input type="button" onclick="UpladFile()" value="上传" />
<input type="button" onclick="cancleUploadFile()" value="取消" />
</body>
</html>