Javascript – jQuery Tips and Tricks

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Syntax

Shorthand for the ready-event by roosteronacid
Line breaks and chainability by roosteronacid
Nesting filters by Nathan Long
Cache a collection and execute commands on the same line by roosteronacid
Contains selector by roosteronacid
Defining properties at element creation by roosteronacid
Access jQuery functions as you would an array by roosteronacid
The noConflict function – Freeing up the $ variable by Oli
Isolate the $ variable in noConflict mode by nickf
No-conflict mode by roosteronacid

Data Storage

The data function – bind data to elements by TenebrousX
HTML5 data attributes support, on steroids! by roosteronacid
The jQuery metadata plug-in by Filip Dupanović

Optimization

Optimize performance of complex selectors by roosteronacid
The context parameter by lupefiasco
Save and reuse searches by Nathan Long
Creating an HTML Element and keeping a reference, Checking if an element exists, Writing your own selectors by Andreas Grech

Miscellaneous

Check the index of an element in a collection by redsquare
Live event handlers by TM
Replace anonymous functions with named functions by ken
Microsoft AJAX framework and jQuery bridge by Slace
jQuery tutorials by egyamado
Remove elements from a collection and preserve chainability by roosteronacid
Declare $this at the beginning of anonymous functions by Ben
FireBug lite, Hotbox plug-in, tell when an image has been loaded and Google CDN by Colour Blend
Judicious use of third-party jQuery scripts by harriyott
The each function by Jan Zich
Form Extensions plug-in by Chris S
Asynchronous each function by OneNerd
The jQuery template plug-in: implementing complex logic using render-functions by roosteronacid

Best Answer

Creating an HTML Element and keeping a reference

var newDiv = $("<div />");

newDiv.attr("id", "myNewDiv").appendTo("body");

/* Now whenever I want to append the new div I created, 
   I can just reference it from the "newDiv" variable */

Checking if an element exists

if ($("#someDiv").length)
{
    // It exists...
}

Writing your own selectors

$.extend($.expr[":"], {
    over100pixels: function (e)
    {
        return $(e).height() > 100;
    }
});

$(".box:over100pixels").click(function ()
{
    alert("The element you clicked is over 100 pixels height");
});

Related Solutions

Javascript – n “exists” function for jQuery

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.

Javascript – Add table row in jQuery

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>');