jQuery - Check if DOM element already exists

This should work for all elements regardless of when they are generated.

if($('some_element').length == 0) {
}

write your code in the ajax callback functions and it should work fine.

This question is about whether an element exists and all answers check if it doesn't exist :) Minor difference but worth mentioning.

Based on jQuery documentation the recommended way to check for existence is

if ($( "#myDiv" ).length) {
    // element exists
}

If you prefer to check for missing element you could use either:

if (!$( "#myDiv" ).length) {
    // element doesn't exist
}

or

if (0 === $( "#myDiv" ).length) {
    // element doesn't exist
}

Note please that in the second option I've used === which is slightly faster than == and put the 0 on the left as a Yoda condition.

Just to confirm that you are selecting the element in the right way. Try this one

if ($('#some_element').length == 0) {
    //Add it to the dom
}