Friday, November 5, 2010

Finding elements using jQuery - Part 2

Today in this post, I am going to pick up from where i left off in the previous post where I discussed about how to use contexts and the usage of the find function and the children function.

Now, lets take a look at another cool way in which a jQuery allows us to traverse the DOM.

One of my favorite functions is the siblings function. This function, as the name suggests allows you to get the siblings of a the current element. For example, suppose you have a unordered list and you need to change the css of a particular list item on mouse hover to indicate that it is being highlighted, but at the same time, you will also need to clear the other list items that were previously hovered over. As is common in jQuery, there is more than one way to achieve this. Lets check out two different ways in which this can be done.

  • a
  • b
  • c

In order to achieve the effect that we desire, we can simply make use of the hover function.


But lets make things a bit more complicated. Suppose instead of simply highlighting the current li, your currently highlighted elements also need to print the information of the previously highlighted element. In this case, the hover function wont suffice. I know example sound a bit silly, but its a silly silly world out there, and requirements can be bizarre and unpredictable. In the next snippet, i am just going to demonstrate how the siblings function can come to the rescue when we need to countenance such requirements.

I am just going to print the value of the previously selected item on the firefox console(ah, yes I am a firefox fan, if you haven't already noticed that by now, although I occasionally use chrome as well for my adventures). Note that I will be printing it when my mouse pointer is over the new element, instead of when the mouse is coming out of the previous element.

      var prevHovered = $(this).siblings(".highlighted");
       console.log("prev html : "+prevHovered.html());

As you see in the above code, I use the mouseover function to handle the selection of the element. The siblings function will select all the siblings of the ul, but the important thing to note here is that the current element is not returned in the selected set. So, all you have is a set of siblings of the current element. You can narrow down the search by providing an optional selector to the siblings function so that only those siblings that match the selected criteria will be returned in the set. However, if you don't pass any argument, all the siblings will be returned.

All the above code did was to select the previously selected element, check if it was not null. It its not, print the html of that element on the console and remove the highlighting from that element.

Easy stuff.

But I mentioned before that I used the mouseover function instead of the hover function. The hover function can take either 1 or 2 arguments as callbacks that can be used to call your function. If only one argument is sent, it will called on both of the mouseover and mouseout event. If you provide two functions as arguments, the first will be used for a mouseover and the second will be used for the mouseout event.

I figured, instead of having an empty mouseout, i'd rather use the mouseover function since it is more natural to our requirement in this case. However you can replace the mouseover function with the single argument hover function in the above code, and it would still work the same.

There's more from where that came from. Stay tuned!

Happy Programming :)
Signing Off

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