my code for getting the Y axis movement on a canvas

My code doesnt work when I use the cursor lock api but does without it
my code:

    function getmouse(event) {
      document.getElementById("canvas_parent").style.top = (event.movementY - (event.movementY *       2)) + "px"
    }

It works the same way with ClientY too so i want it to change the value of event.movementY