CODEWITHSUNDEEP
jquery
Samantha J T Star
Samantha J T Star

Reputation: 32758

How can I code a check to see if an element is first or last of a parent?

I have the following menu which can have anything up to about 50 items and two links that a user can use to navigate to the previous or next city. Here for this example I am just showing four address links.

<ul id="menu">
   <li><a href="/City/0101004H">1</a></li>
   <li><a href="/City/0101004I">2</a></li>
   <li><a href="/City/0101004J">3</a></li>
   <li><a href="/City/0101004K">4</a></li>
</ul>

<a id="prev" href="#"><img width="16" height="16" src="/images/prev.png">Prev</a>
<a id="next" href="#"><img width="16" height="16" src="/images/next.png">Next</a>

I had some help on stack overflow and came up with the following code:

fiddle

$("#menu").on('click', 'a[href^="/City"]', function(event) {
   event.preventDefault();
      var prev = $(this).parent().prev().find('a');
      var next = $(this).parent().next().find('a');
      $('#prev').prop('href', jQuery(prev).prop('href')).prop('title', 'City ' + jQuery(prev).text());
      $('#next').prop('href', jQuery(next).prop('href')).prop('title', 'City ' + jQuery(next).text())
});

This sets the href of the previous and next to the appropriate value when I click on on one of the menu items. It works but not for the first and last items in the list. What I need is this:

a) When the first item is clicked on I would like the #prev to change to:

<a id="prev" href="#"><img src="/images/noentry.png"></a>

b) When the last item is clicked on I would like the #next to change to:

<a id="next" href="#"><img src="/images/noentry.png"></a>

Is there an easy way I could do this without adding too much additional code?

Upvotes: 7

Views: 215

Answers (4)

Sampson
Sampson

Reputation: 268344

You can test if the element is the first child, or the last child using the following:

$(this).parent().is(":first-child");
$(this).parent().is(":last-child");

If this referenced the a being clicked, we would test whether it was the first link, or the last link in the list by testing whether or not its parent was a first child, or a last child, or neither.

Additionally, you could base attribute-object-construction off of these values:

$("#menu").on('click', 'a', function(event) {

   // Prevent link from taking us anywhere
   event.preventDefault();

   // We'll be referencing the parent numerous times
   var parent = $(this).parent();

   // Determine the new properties of the PREV link
   var prev = parent.is(":first-child") 
       ? { html: '<img src="/images/noentry.png" />', 
           title: null } 
       : { html: '<img src="/images/prev.png" /> Prev', 
           title: 'City ' + parent.prev().text() } ;

   // Determine the new properties of the NEXT link
   var next = parent.is(":last-child") 
       ? { html: '<img src="/images/noentry.png" />', 
           title: null } 
       : { html: '<img src="/images/next.png" /> Next', 
           title: 'City ' + parent.next().text() } ;

    // Set new attribtes of both PREV and NEXT
    $("#prev").attr( prev );
    $("#next").attr( next );

});​

You could further construct the attributes for the #prev and #next elements to your needs.

Demo: http://jsfiddle.net/MX94J/1/

Upvotes: 10

jfriend00
jfriend00

Reputation: 707218

You can check the jQuery object length for zero and act accordingly:

$("#menu").on('click', 'a[href^="/City"]', function(event) {
      event.preventDefault();
      var pHref, nHref, pTitle, nTitle;
      var prev = $(this).parent().prev().find('a');
      var next = $(this).parent().next().find('a');
      if (prev.length == 0) {
          pHref = "#";
          pTitle = "";
      } else {
          pHref = prev.prop('href');
          pTitle = prev.prop('City' prev.text());
      }
      if (next.length == 0) {
          nHref = "#";
          nTitle = "";
      } else {
          nHref = next.prop('href');
          nTitle = next.prop('City' prev.text());
      }

      $('#prev').prop('href', pHref).prop('title', pTitle);
      $('#next').prop('href', nHref).prop('title', nTitle)
});

or a little cleaner with a local function to do the work:

("#menu").on('click', 'a[href^="/City"]', function(event) {

      function setProps(targetSelector, srcObject) {
          var href, title;
          if (srcObject.length) {
              href = srcObject.prop('href');
              title = srcObject.prop('title');
          } else {
              href = "#";
              title = "";
          }
          $(targetSelector).prop('href', href).prop('title', title);
      }

      event.preventDefault();
      var p = $(this).parent();
      setProps('#prev', p.prev().find('a'));
      setProps('#next', p.next().find('a'));
});

Upvotes: 1

lucuma
lucuma

Reputation: 18339

An alternate way to do this is the following using an index instead or properties:

http://jsfiddle.net/QrE6u/1/

var index = 0;
var nElements = $('#menu a').length;

$('#menu a').click(function(e) {
    e.preventDefault();
    index = $(this).parents('ul').find('a').index(this);
    if (index==0) {
       $('#prev img').attr('src', '/images/noentry.png');
    } 
    if (index==nElements-1) {
      $('#next img').attr('src', '/images/noentry.png');

    }
    alert(index);
});

    $('#prev').click(function() {
      index = (index - 1) % nElements;
      $('#menu a').eq(index).click();
    }); 
    $('#next').click(function() {
      index = (index + 1)% nElements;
      $('#menu a').eq(index).click();
    });
​

Upvotes: 1

Matt Ball
Matt Ball

Reputation: 359776

If an element elt is the first of its siblings, $(elt).prev().length will be 0.
If an element elt is the last of its siblings, $(elt).next().length will be 0.

Upvotes: 1

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