using .each() to iterate over selections for HTML5 <figure> and <figcaption>

Greetings all,

I've written a script to create HTML5 image captions from regular image tags using <figure> and <figcaption>.

My CMS uses FCKEditor, which always places embedded images inside of paragraphs. So my script builds a <figcaption> around the image and then moves it outside of the paragraph (see html5, figure/figcaption inside a paragraph gives unpredictable output)).

The script I wrote works, but it traverses the DOM twice 'cause I couldn't figure out a way to traverse the DOM only once. I'd appreciate if someone better versed at JQuery could offer some suggestions on how to simplify/improve the script.

Thanks, -NorthK

// use like this: 
// <img cl开发者_StackOverflow中文版ass="caption" src="http://placehold.it/350x150" alt="Sample image caption" />
//
$(document).ready(function() {
// iterate over each element with img.caption
$('img.caption').each(function() {
    var classList = $(this).attr('class');  // grab the image's list of classes, if any
    $(this).wrap('<figure class="' + classList + '"></figure>'); // wrap the <img> with <figure> and add the saved classes
    $(this).after('<figcaption>' + $(this).attr('alt') + '</figcaption>'); // add the caption
    $(this).removeAttr('class'); // remove the classes from the original <img> element
});

// now iterate over each figure.caption we built, and relocate it to before its closest preceding paragraph
$('figure.caption').each(function() {
    $(this).parent('p').before($(this));
});
})

As you wrap each element, you can save the wrapper in an array, then process the array rather than re-traversing the DOM:

$(document).ready(function() {
    var wrappers = [];

    // iterate over each element with img.caption
    $('img.caption').each(function() {
        var $this = $(this);
        var classList = this.className;  // grab the image's list of classes, if any
        $this.wrap('<figure class="' + classList + '"></figure>'); // wrap the <img> with <figure> and add the saved classes

        // Remember the wrapper here:
        wrappers.add($this.parent());

        $this.after('<figcaption>' + $(this).attr('alt') + '</figcaption>'); // add the caption
        $this.removeAttr('class'); // remove the classes from the original <img> element
    });

    // now iterate over each figure.caption we built, and relocate it to before its closest preceding paragraph
    $.each(wrappers, function(index, item) {
        $(item).parent('p').before(item);
    });

    // And if you're done with it, release it:
    wrappers = null;
});

Here's a simplified example:

HTML:

<p><img class='caption' src='http://www.gravatar.com/avatar/6d8ebb117e8d83d74ea95fbdd0f87e13?s=48&d=identicon&r=PG'></p>
<p><img class='caption' src='http://www.gravatar.com/avatar/ca3e484c121268e4c8302616b2395eb9?s=48&d=identicon&r=PG'</p>

JavaScript:

jQuery(function($) {

  var wrappers = [];
  $("img.caption").each(function() {
    var $this = $(this);
    $this.wrap("<figure class='" + this.className + "'>");
    wrappers.push($this.parent('figure'));
  });
  $.each(wrappers, function(index, item) {
    $(item).addClass("foo");
  });
  wrappers = null;
});

Live copy

Off-topic: You seem to be interested in efficiency, so I'll mention: Every call to $(this) requires multiple function calls and a memory allocation. Rather than doing it repeatedly, do it once on each loop and cache the result. I've done that in the above as an example. Constantly writing $(this) in the same function isn't ideal from a performance perspective, although in 99% of cases, it doesn't matter. If you're dealing with a lot of elements, it does.

You can use the unwrap method to get rid of the <p> in the first iteration. You can also use chaining to simplify the syntax.

$('.caption').each(function() {
    $(this)
        .unwrap() // ditch the conflicting pararaph parent wrapper
        .wrap('<figure class="' + $(this).attr('class') + '" />') // wrap the figure tag instead, jQuery can handle a self closing tag
        .after('<figcaption>' + $(this).attr('alt') + '</figcaption>') // add the caption
        .removeAttr('class'); // remove the classes from the original <img> element
});

http://jsfiddle.net/pxfunc/AGgL2/