setting a flag, so that the first movement will have the correct value

[jasonwilliams]

This should hopefully fix the initial movementX and movementY values introduced in #9018

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[gaearon]

Out of curiosity, can you make some browser testing and see what browser gives us for the first event, when this property is supported natively?

[nhunzaker]

As far as I can tell, the initial movement is always 0, using this method:

1. Open the /mouse-events fixture
2. Refresh the page, and immediately alt+tab to another app
3. Hover over the fixture
4. Tab back to the browser
5. Move your mouse

[nhunzaker]

As far as I can tell, this looks correct. However I will not be able to test in IE until tomorrow morning (Airplane wifi :()

[nhunzaker]

This does, however, appear to work correctly in Safari 11.1 (Safari is the other browser that does not support movementX/Y)

[gaearon]

LGTM

[jasonwilliams]

@gaearon @nhunzaker
I've tested Chrome, Firefox and Edge, by using the mouse-event fixture, setting a breakpoint over https://github.com/facebook/react/blob/master/packages/react-dom/src/events/SyntheticMouseEvent.js#L45 and then hovering over the page after page load.

Chrome 67.0.3396.87 i did quite a few times, and the first hover event always had movementX at 0

Edge 42.17134.1.0 had very similar results after quite a few tries

Firefox Developer Edition 61.0b14 seemed to be the outlier here, as i was getting random values each time, sometimes 13, or 18 or 12. This could be saying more about dev tools though, rather than the initial value of movementX

[gaearon]

Nice! This is sufficient—I think 0 is the most reasonable initial value.

[aweary]

0 is the spec-defined initial value 👍

https://w3c.github.io/pointerlock/#extensions-to-the-mouseevent-interface

The un-initialized value of movementX/Y must be 0.

I also noticed that the spec states:

movementX/Y must be zero for all mouse events except mousemove.

It's potentially minor but we're not restricting our polyfill mousemove events, so it's slightly out of spec.

[gaearon]

It's potentially minor but we're not restricting our polyfill mousemove events, so it's slightly out of spec.

Oh, I missed that. We should definitely limit it to mousemove events. I don't think it's minor—if you rely on movementX/movementY then you'll potentially drop movements.

[aweary]

@jasonwilliams do you want to fix this in another follow up?

[jasonwilliams]

Yup I missed that too, I can take a look