概述：ajax提交比较大的文件的时候，我们希望能够看到它上传的进度，代码放下面了。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>XMLHttpRequest 上传文件进度条示例</title>
</head>
<body>
<progress id="upload_progress" value="0" max="100"></progress>
<input id="upload_file" type="file" name="upload_file" />
<button id="btn_start">Start</button>
<button id="btn_cancel">Cancel</button>
<script type="text/javascript" src="/res/lib/jquery-1.11.3.js"></script>
<script type="text/javascript">
var xhr = new XMLHttpRequest();
var progressBar = document.getElementById('upload_progress');
$('#btn_start').click(function() {
var uploadFile = document.getElementById('upload_file').files[0];
var formData = new FormData();
formData.append('upload_file', uploadFile); // ---------------------------------------
// 原生xmlHttpRequest发送
xhr.open('post', '/server_url.php');
xhr.onload = function() {
alert('完成！');
};
xhr.onerror = function() {
alert('无法连接服务器！');
};
xhr.upload.onprogress = function(progress) {
if (progress.lengthComputable) {
console.log(progress.loaded / progress.total * 100);
progressBar.max = progress.total;
progressBar.value = progress.loaded;
}
};
xhr.upload.onloadstart = function() {
console.log('started...');
};
xhr.send(formData); // ---------------------------------------
// 使用jQuery发送
/**
$.ajax({
type: "POST",
url: "/server_url.php",
data: formData , //这里上传的数据使用了formData 对象
processData: false,
contentType: false, //必须false才会自动加上正确的Content-Type
//这里我们先拿到jQuery产生的 XMLHttpRequest对象，为其增加 progress 事件绑定，然后再返回交给ajax使用
xhr: function() {
var xhr = $.ajaxSettings.xhr();
if (xhr.upload) {
xhr.upload.onprogress = function(progress) {
if (progress.lengthComputable) {
console.log(progress.loaded / progress.total * 100);
progressBar.max = progress.total;
progressBar.value = progress.loaded;
}
};
xhr.upload.onloadstart = function() {
console.log('started...');
};
}
return xhr;
}
}).done(function(resp) {
alert('完成！');
}).fail(function(err) {
alert('无法连接服务器！')
});*/ }); $('#btn_cancel').click(function() {
xhr.abort();
});
</script>
</body>
</html>
原理就是这样，需要在此基础上做扩展的可以随意添加自己想要的功能。