Question

I need check every .archive_blocks for containing .archive_blocks_fa_active.
If is it true, apply css to .archive_blocks_sa.

<div class="archive_blocks">
    <a href="#" class="archive_blocks_fa_active">
        <img width="142" height="142" src="#">
    </a>
    <div class="archive_blocks_name">
        <a href="#" class="archive_blocks_sa">Ilustrations</a>
    </div>
</div>

JQUERY:

 $('.archive_blocks').each(function(){

    if ( $("a.archive_blocks_fa_active").parents(this).length == 1 ) { 
        alert('OK'); 
    } else {        
        alert('NO');    
    }
});

Answer 1

Assuming I’ve understood your question correctly, can’t you just do this and not bother with the each:

$(".archive_blocks a.archive_blocks_fa_active")
    .closest(".archive_blocks")
    .find(".archive_blocks_sa")
    .addClass("whatever");

This uses a descendant selector which matches any a.archive_blocks_fa_active element that is a descendant of an .archive_blocks element. It then finds the related .archive_blocks_sa (there would be other ways of doing that, perhaps using parent and next if you prefer) and then adds the class.