In JavaScript, everything is 'truthy' or 'falsy', and for numbers 0
means false
, everything else true
. So you could write:
if ($(selector).length)
You don't need that >0
part.
With HTML5 you can make file uploads with Ajax and jQuery. Not only that, you can do file validations (name, size, and MIME type) or handle the progress event with the HTML5 progress tag (or a div). Recently I had to make a file uploader, but I didn't want to use Flash nor Iframes or plugins and after some research I came up with the solution.
The HTML:
<form enctype="multipart/form-data">
<input name="file" type="file" />
<input type="button" value="Upload" />
</form>
<progress></progress>
First, you can do some validation if you want. For example, in the .on('change')
event of the file:
$(':file').on('change', function () {
var file = this.files[0];
if (file.size > 1024) {
alert('max upload size is 1k');
}
// Also see .name, .type
});
Now the $.ajax()
submit with the button's click:
$(':button').on('click', function () {
$.ajax({
// Your server script to process the upload
url: 'upload.php',
type: 'POST',
// Form data
data: new FormData($('form')[0]),
// Tell jQuery not to process data or worry about content-type
// You *must* include these options!
cache: false,
contentType: false,
processData: false,
// Custom XMLHttpRequest
xhr: function () {
var myXhr = $.ajaxSettings.xhr();
if (myXhr.upload) {
// For handling the progress of the upload
myXhr.upload.addEventListener('progress', function (e) {
if (e.lengthComputable) {
$('progress').attr({
value: e.loaded,
max: e.total,
});
}
}, false);
}
return myXhr;
}
});
});
As you can see, with HTML5 (and some research) file uploading not only becomes possible but super easy. Try it with Google Chrome as some of the HTML5 components of the examples aren't available in every browser.
Best Answer
An UpdatePanel completely replaces the contents of the update panel on an update. This means that those events you subscribed to are no longer subscribed because there are new elements in that update panel.
What I've done to work around this is re-subscribe to the events I need after every update. I use
$(document).ready()
for the initial load, then use Microsoft'sPageRequestManager
(available if you have an update panel on your page) to re-subscribe every update.The
PageRequestManager
is a javascript object which is automatically available if an update panel is on the page. You shouldn't need to do anything other than the code above in order to use it as long as the UpdatePanel is on the page.If you need more detailed control, this event passes arguments similar to how .NET events are passed arguments
(sender, eventArgs)
so you can see what raised the event and only re-bind if needed.Here is the latest version of the documentation from Microsoft: msdn.microsoft.com/.../bb383810.aspx
A better option you may have, depending on your needs, is to use jQuery's
.on()
. These method are more efficient than re-subscribing to DOM elements on every update. Read all of the documentation before you use this approach however, since it may or may not meet your needs. There are a lot of jQuery plugins that would be unreasonable to refactor to use.delegate()
or.on()
, so in those cases, you're better off re-subscribing.