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
Here's your example in the "one" line.
Update: I thought I'd update this post since it still gets quite a bit of traffic. In the comments below there's some discussion about
$("<div>")
vs$("<div></div>")
vs$(document.createElement('div'))
as a way of creating new elements, and which is "best".I put together a small benchmark, and here are roughly the results of repeating the above options 100,000 times:
jQuery 1.4, 1.5, 1.6
jQuery 1.3
jQuery 1.2
I think it's no big surprise, but
document.createElement
is the fastest method. Of course, before you go off and start refactoring your entire codebase, remember that the differences we're talking about here (in all but the archaic versions of jQuery) equate to about an extra 3 milliseconds per thousand elements.Update 2
Updated for jQuery 1.7.2 and put the benchmark on
JSBen.ch
which is probably a bit more scientific than my primitive benchmarks, plus it can be crowdsourced now!http://jsben.ch/#/ARUtz