How to Set Focus on Input Field using JQuery

If the input happens to be in a bootstrap modal dialog, the answer is different. Copying from How to Set focus to first text input in a bootstrap modal after shown this is what is required:

$('#myModal').on('shown.bs.modal', function () {
  $('#textareaID').focus();
})  

Try this, to set the focus to the first input field:

$(this).parent().siblings('div.bottom').find("input.post").focus();