Offscreen add attach

[sammy-SC]

Offscreen.attach is imperative API to signal to Offscreen that its updates should be high priority and effects should be mounted. Coupled with Offscreen.detach it gives ability to manually control Offscreen. Unlike with mode visible and hidden, it is developers job to make sure contents of Offscreen are not visible to users.
Offscreen.attach only works if mode is manual.

Example uses:

let offscreenRef = useRef(null);
<Offscreen mode={'manual'} ref={offscreenRef)}>
  <Child />
</Offscreen>

// ------

// Offscreen is attached by default. 
// For example user scrolls away and Offscreen subtree is not visible anymore.
offscreenRef.current.detach();


// User scrolls back and Offscreen subtree is visible again.
offscreenRef.current.attach();

[sizebot]

Comparing: b14d7fa...dad8f0c

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	+0.14%	154.37 kB	154.58 kB	+0.07%	48.97 kB	49.01 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	+0.14%	156.29 kB	156.51 kB	+0.05%	49.63 kB	49.65 kB
facebook-www/ReactDOM-prod.classic.js	+0.11%	533.12 kB	533.71 kB	+0.08%	94.96 kB	95.04 kB
facebook-www/ReactDOM-prod.modern.js	+0.11%	518.22 kB	518.81 kB	+0.10%	92.76 kB	92.85 kB
facebook-www/ReactDOMForked-prod.classic.js	+0.11%	533.12 kB	533.71 kB	+0.08%	94.96 kB	95.04 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable-semver/react-art/cjs/react-art.production.min.js	+0.29%	92.26 kB	92.53 kB	+0.25%	28.38 kB	28.45 kB
oss-stable/react-art/cjs/react-art.production.min.js	+0.29%	92.29 kB	92.55 kB	+0.25%	28.38 kB	28.45 kB
oss-experimental/react-art/cjs/react-art.production.min.js	+0.28%	93.70 kB	93.97 kB	+0.22%	28.83 kB	28.89 kB
facebook-www/ReactART-prod.modern.js	+0.23%	324.92 kB	325.66 kB	+0.20%	55.37 kB	55.48 kB
facebook-www/ReactART-prod.classic.js	+0.22%	335.87 kB	336.60 kB	+0.18%	57.28 kB	57.39 kB
oss-stable-semver/react-test-renderer/umd/react-test-renderer.production.min.js	+0.21%	100.21 kB	100.42 kB	+0.11%	31.07 kB	31.10 kB
oss-stable/react-test-renderer/umd/react-test-renderer.production.min.js	+0.21%	100.23 kB	100.44 kB	+0.10%	31.07 kB	31.10 kB
oss-experimental/react-test-renderer/umd/react-test-renderer.production.min.js	+0.21%	100.29 kB	100.50 kB	+0.10%	31.10 kB	31.13 kB
oss-stable-semver/react-test-renderer/cjs/react-test-renderer.production.min.js	+0.21%	99.97 kB	100.18 kB	+0.16%	30.66 kB	30.71 kB
oss-stable/react-test-renderer/cjs/react-test-renderer.production.min.js	+0.21%	99.99 kB	100.20 kB	+0.16%	30.66 kB	30.71 kB
oss-experimental/react-test-renderer/cjs/react-test-renderer.production.min.js	+0.21%	100.05 kB	100.26 kB	+0.16%	30.69 kB	30.74 kB
oss-stable-semver/react-art/umd/react-art.production.min.js	+0.21%	128.10 kB	128.37 kB	+0.26%	39.54 kB	39.64 kB
oss-stable/react-art/umd/react-art.production.min.js	+0.21%	128.13 kB	128.39 kB	+0.26%	39.54 kB	39.64 kB
oss-experimental/react-art/umd/react-art.production.min.js	+0.21%	129.53 kB	129.80 kB	+0.19%	40.00 kB	40.08 kB
react-native/implementations/ReactFabric-prod.fb.js	+0.20%	327.70 kB	328.37 kB	+0.18%	58.17 kB	58.28 kB
oss-stable-semver/react-reconciler/cjs/react-reconciler.production.min.js	+0.20%	106.11 kB	106.32 kB	+0.10%	32.25 kB	32.28 kB
oss-stable/react-reconciler/cjs/react-reconciler.production.min.js	+0.20%	106.13 kB	106.35 kB	+0.10%	32.27 kB	32.30 kB
react-native/implementations/ReactNativeRenderer-prod.fb.js	+0.20%	333.50 kB	334.17 kB	+0.15%	59.12 kB	59.21 kB

Generated by 🚫 dangerJS against dad8f0c

[acdlite]

Since all this does now is schedule an update, you don't need the scheduleMicrotask call

[sammy-SC]

I was using scheduleMicrotask to postpone detachment of Offscreen if detach is called in an effect or in render phase. I'm not sure how to do that with scheduleUpdateOnFiber. This is probably just an optimisation.

[acdlite]

This looks good to me now but let's wait a day or two before landing in case there's an issue with the sync