How to remove event listener on layout separator

I want to change the separator to button and remove the separator mousedown event listener.

I try this.

  1. document.getElementsByClassName(“dhxlayout_sep dhxlayout_sep_resize_v”).onmousedown = “”;
  2. document.getElementsByClassName(“dhxlayout_sep dhxlayout_sep_resize_v”).removeEventListener(‘mousedown’,_doOnMouseDown);
  3. $(“.dhxlayout_sep”).off(‘mousedown’);
  4. $(“.dhxlayout_sep”).unbind(‘mousedown’);

is don’t have The mousedown event function name?
how I can remove the separator event listener?