Question

$("#main .primary")
        .width($(this).closest("#main .row")
        .outerWidth(true) - $(this).closest("#main .secondary")
        .outerWidth(true));

..doesn’t work at all.

What I’m doing is applying the width to the primary div by subtracting the width of secondary from main (parent).

<div id="main">
    <div class="row">
        <div class="primary"></div>
        <div class="secondary"></div>
    </div>
</div>

Thanks

Answer 1

First the selector #main .row will return an empty jQuery Object,
if you want to match the element having an id and a class together you can use it like this :

#myId.my-class // Select by id and class
div#myId.my-class // Select by element and the id and the class

I suggest for you to use the siblings() method in your case

$('#main .primary')
  .width( function(){ 
   return $(this).closest('.row').width() - // or you can use .parent() instead
          $(this).siblings('.secondary').outerWidth(true); 
})