5 examples of 'useeffect previous state' in JavaScript

3
export default function usePrevious(value) {
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  const ref = useRef();
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  useEffect(() => {
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    ref.current = value;
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  });
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  return [ref.current];
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}

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_applyEffect() {
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  super._applyEffect();
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  const player = this.game.player;
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  this.effectTypes.forEach((effectType) => {
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    const amount = this._getAmountForEffect(effectType);
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    if(amount !== null) {
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      const event = Mediator.publish(EffectItemMessages.APPLY, {
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        source: this.entity,
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        effectType: effectType,
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        amount: amount
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      });
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      if(event.process) {
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        switch (event.args.effectType) {
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          case ItemEffectType.HEALTH:
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            player.increaseHealth(event.args.amount);
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            break;
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          case ItemEffectType.POINTS:
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            player.increasePoints(event.args.amount);
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            break;
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          case ItemEffectType.MONEY:
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            player.increaseMoney(event.args.amount);
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            break;
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        }
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      }
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    }
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  });
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}

82
function effectCurrent( func ) {
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	chrome.tabs.query( {}, function( s ) { 
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		let activeIndex = -1;
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		for( let i = 0; i < s.length; i++ ) {
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			if ( s[i].active ) {
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				activeIndex = i;
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				break;
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			}
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		}
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		if ( activeIndex >= 0 ) {
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			// tab, tab index, tab id
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			func( s[activeIndex], activeIndex, s[activeIndex].id );
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		}
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	} );
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}

51
function Effect() {
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  const { gl, scene, camera, size } = useThree()
53
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  const [bloom, final] = useMemo(() => {
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    const renderScene = new RenderPass(scene, camera)
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    const comp = new EffectComposer(gl)
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    comp.renderToScreen = false
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    comp.addPass(renderScene)
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    comp.addPass(new UnrealBloomPass(new THREE.Vector2(size.width, size.height), 1.25, 1, 0))
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    const finalComposer = new EffectComposer(gl)
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    finalComposer.addPass(renderScene)
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    const finalPass = new ShaderPass(
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      new THREE.ShaderMaterial({
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        uniforms: { baseTexture: { value: null }, bloomTexture: { value: comp.renderTarget2.texture } },
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        vertexShader:
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          'varying vec2 vUv; void main() { vUv = uv; gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 ); }',
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        fragmentShader:
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          'uniform sampler2D baseTexture; uniform sampler2D bloomTexture; varying vec2 vUv; vec4 getTexture( sampler2D texelToLinearTexture ) { return mapTexelToLinear( texture2D( texelToLinearTexture , vUv ) ); } void main() { gl_FragColor = ( getTexture( baseTexture ) + vec4( 1.0 ) * getTexture( bloomTexture ) ); }',
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      }),
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      'baseTexture'
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    )
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    finalPass.needsSwap = true
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    finalComposer.addPass(finalPass)
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    const fxaa = new ShaderPass(FXAAShader)
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    fxaa.material.uniforms['resolution'].value.x = 1 / size.width
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    fxaa.material.uniforms['resolution'].value.y = 1 / size.height
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    finalComposer.addPass(fxaa)
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    return [comp, finalComposer]
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  }, [])
84
85
  useEffect(() => {
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    bloom.setSize(size.width, size.height)
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    final.setSize(size.width, size.height)
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  }, [bloom, final, size])
89
90
  useFrame(() => {
91
    // https://github.com/mrdoob/three.js/blob/master/examples/webgl_postprocessing_unreal_bloom_selective.html
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    // this seems kinda dirty, it mutates the scene and overwrites materials
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    scene.traverse(darkenNonBloomed)
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    bloom.render()
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    scene.traverse(restoreMaterial)
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    // then writes the normal scene on top
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    final.render()
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  }, 1)
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  return null
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}

82
effect(value) {
83
  this.lightState.effect(value);
84
  return this;
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}