Chrome Version       : 63.0.3239.132
OS Version: 10.0
URLs (if applicable) : https://stackoverflow.com/questions/47985847/javascript-mouseevent-movementx-and-movementy-large-spikes
Other browsers tested:
  Add OK or FAIL after other browsers where you have tested this issue:
     Safari:
    Firefox: OK
    IE/Edge: OK

What steps will reproduce the problem?
1. pointerLock when mouse pointer is at the centre of the element, move slowly but not far away, works fine, values are small, < 10
2. pointerLock near the edge of the element, move slowly toward the edge, notice jump in MovementX or MovementY values, probably depends on the element size

What is the expected result? 
as in Repro step #1

What happens instead of that?
as in Repro step #2

Please provide any additional information below. Attach a screenshot if
possible.

UserAgentString: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36