Javascript – jQuery to find all previous elements that match an expression

javascriptjquery

Using jQuery, how do you match elements that are prior to the current element in the DOM tree? Using prevAll() only matches previous siblings.

eg:

<table>
    <tr>
        <td class="findme">find this one</td>
    </tr>
    <tr>
        <td><a href="#" class="myLinks">find the previous .findme</a></td>
    </tr>
    <tr>
        <td class="findme">don't find this one</td>
    </tr>
</table>

In my specific case, I'll be searching for the first .findme element prior to the link clicked.

Best Solution

Ok, here's what I've come up with - hopefully it'll be useful in many different situations. It's 2 extensions to jQuery that I call prevALL and nextALL. While the standard prevAll() matches previous siblings, prevALL() matches ALL previous elements all the way up the DOM tree, similarly for nextAll() and nextALL().

I'll try to explain it in the comments below:

// this is a small helper extension i stole from
// http://www.texotela.co.uk/code/jquery/reverse/
// it merely reverses the order of a jQuery set.
$.fn.reverse = function() {
    return this.pushStack(this.get().reverse(), arguments);
};

// create two new functions: prevALL and nextALL. they're very similar, hence this style.
$.each( ['prev', 'next'], function(unusedIndex, name) {
    $.fn[ name + 'ALL' ] = function(matchExpr) {
        // get all the elements in the body, including the body.
        var $all = $('body').find('*').andSelf();

        // slice the $all object according to which way we're looking
        $all = (name == 'prev')
             ? $all.slice(0, $all.index(this)).reverse()
             : $all.slice($all.index(this) + 1)
        ;
        // filter the matches if specified
        if (matchExpr) $all = $all.filter(matchExpr);
        return $all;
    };
});

usage:

$('.myLinks').click(function() {
    $(this)
        .prevALL('.findme:first')
        .html("You found me!")
    ;

    // set previous nodes to blue
    $(this).prevALL().css('backgroundColor', 'blue');

    // set following nodes to red
    $(this).nextALL().css('backgroundColor', 'red');
});

edit - function rewritten from scratch. I just thought of a much quicker and simpler way to do it. Take a look at the edit history to see my first iteration.

edit again - found an easier way to do it!