Question

I have a variable that I would like to not affect condition or donot charge when necessary, ie when not in this case the DIV # sidebar

My code is:

var top = $('#sidebar').offset().top - parseFloat($('#sidebar').css('margin-top').replace(/auto/, 0));
var _height = $('#sidebar').height();
var _original_top = $('#sidebar').offset().top;
$(window).scroll(function(event) {
    var y = $(this).scrollTop();
    var z = $('footer').offset().top;
    if (y >= top && (y + _height) < z) {
        $('#sidebar').removeClass('stuck-bottom').addClass('fixed');
    } else {
        if ((y + _height) > z) {
            $('#sidebar').removeClass('fixed').addClass('stuck-bottom');
        }
        else $('#sidebar').removeClass('stuck-bottom').removeClass('fixed');
    }
});

If I put this code does not work: (

if ($('#sidebar')) { ... }

Answer 1

If the problem is that your if always executes the code, you need to change how you detect if #sidebar exists. This may be because $('#sidebar') will usually evaluate to true, even if there are no matching elements, because $() returns a valid jQuery object. To have the condition only succeed when #sidebar actually exists, try:

if ($('#sidebar').length) { ... }

However, if your problem is that the condition never succeeds even if #sidebar exists, your code may be getting executed before the DOM has loaded. You’ll need to wrap your code in a $.ready() function, so it doesn’t execute until the page has been downloaded, parsed and rendered:

jQuery(function($) {
    if ($('#sidebar').length) { ... }
});