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.
The approach you suggest is not guaranteed to give you the result you're looking for - what if you had a tbody for example:
<table id="myTable">
<tbody>
<tr>...</tr>
<tr>...</tr>
</tbody>
</table>
You would end up with the following:
<table id="myTable">
<tbody>
<tr>...</tr>
<tr>...</tr>
</tbody>
<tr>...</tr>
</table>
I would therefore recommend this approach instead:
$('#myTable tr:last').after('<tr>...</tr><tr>...</tr>');
You can include anything within the after() method as long as it's valid HTML, including multiple rows as per the example above.
Update: Revisiting this answer following recent activity with this question. eyelidlessness makes a good comment that there will always be a tbody in the DOM; this is true, but only if there is at least one row. If you have no rows, there will be no tbody unless you have specified one yourself.
DaRKoN_ suggests appending to the tbody rather than adding content after the last tr. This gets around the issue of having no rows, but still isn't bulletproof as you could theoretically have multiple tbody elements and the row would get added to each of them.
Weighing everything up, I'm not sure there is a single one-line solution that accounts for every single possible scenario. You will need to make sure the jQuery code tallies with your markup.
I think the safest solution is probably to ensure your table always includes at least one tbody in your markup, even if it has no rows. On this basis, you can use the following which will work however many rows you have (and also account for multiple tbody elements):
$('#myTable > tbody:last-child').append('<tr>...</tr><tr>...</tr>');
Best Answer
jQuery is purely designed to simplify and standardise scripting across browsers. It focuses on the low-level stuff: creating elements, manipulating the DOM, managing attributes, performing HTTP requests, etc.
jQueryUI is a set of user interface components & features built on top of jQuery (i.e. it needs jQuery to work): buttons, dialog boxes, sliders, tabs, more advanced animations, drag/drop functionality.
jQuery and jQueryUI are both designed to be 'added' to your site (desktop or mobile) - if you want to add a particular feature, jQuery or jQueryUI might be able to help.
jQuery Mobile, however, is a full framework. It's intended to be your starting point for a mobile site. It requires jQuery and makes use of features of both jQuery and jQueryUI to provide both UI components and API features for building mobile-friendly sites. You can still use as much or as little of it as you like, but jQuery Mobile can control the whole viewport in a mobile-friendly way if you let it.
Another major difference is that jQuery and jQueryUI aim to be a layer on top of your HTML and CSS. You should be able to just leave your markup alone and enhance it with jQuery. However, jQuery Mobile provides ways to define where you want components to appear using HTML alone - e.g. (from the jQuery Mobile site):
The
data-roleattribute tells jQuery Mobile to turn this list into a mobile-friendly UI component and thedata-insetanddata-filterattributes set properties of that - without writing a single line of JavaScript. jQueryUI components, on the other hand, are normally created by writing a few lines of JavaScript to instantiate the component in the DOM.