Question

Using jQuery, I would like to extract a number from a <span> and use it to calculate a new value.

<div class="post-100" data-postid="100">
   <span class="score">3</span>
</div>

I’ve got the general Idea, but I can’t figure out how to reference the existing span value:

if (response.newvoteid == null)
{
    $(".post-" + $(this).data("postid") + " .score").text(
            parseInt( **EXISTING VALUE + 1 OR -1**));
}

Update: I am now using the following which fails to calculate the new value, but simply adds a number to the text. For example, <span class="score">3</span> becomes <span class="score">31</span>

var number = $(".post-" + $(this).data("postId") + " .score").text();
$(".post-" + $(this).data("postId") + " .score").text(number + 1);

Answer 1

Just pass a function to .text() that returns the old value incremented (or decremented):

$(".post-" + $(this).data("postid") + " .score").text( function( i, txt ) {
    return ( parseInt( txt, 10 ) + 1 ); // Returns the old value,
});                                     //      plus (or minus) 1.