useEffect not getting dependency value updated

Question

I have a component that I want to edit some style dynamically. When I enter the component I want it to smoothly grow and when I leave I want it to smoothly shorten.

This is my code:

  const easing = 0.1;
  const outScale = 0.6;
  const inScale = 1;
  let targetScale = outScale;
  let elementScale = targetScale;
  let innerScale = 1 / elementScale;

  const [parentTransformStyle, setParentTransformStyle] = useState(
    `scale(${elementScale})`
  );
  const [innerTransformStyle, setInnerTransformStyle] = useState(
    `scale(${innerScale})`
  );
  const requestRef = useRef();

  const onPointOverEvent = () => {
    targetScale = inScale;
    console.log("over", inScale, targetScale);
  };

  const onPointerOutEvent = () => {
    targetScale = outScale;
    console.log("out", outScale, targetScale);
  };

  const animate = () => {
    console.log("animate", targetScale);

    elementScale += (targetScale - elementScale) * easing;
    innerScale = 1 / elementScale;

    setParentTransformStyle(`scale(${elementScale})`);
    setInnerTransformStyle(`scale(${innerScale})`);

    requestAnimationFrame(animate);
  };

  useEffect(() => {
    requestRef.current = requestAnimationFrame(animate);
    return () => cancelAnimationFrame(requestRef.current);
  }, []);

The variable targetScale is supposed to be updated when the mouse hovers in the element and when the mouse leaves the element.

If I print the value inside the event listeners, the value is correct. However inside the animate function, it has the initial value. Can someone point me to what I'm missing?

Soc · Accepted Answer · 2020-02-04 00:31:31Z

2

Is there any reason you can't use CSS transformations instead of doing the animation yourself?

Example:

function MyComponent() {
  const [innerTransformStyle, setInnerTransformStyle] = React.useState(
    `scale(${0.6})`
  );

  const onPointOverEvent = () => {
    setInnerTransformStyle(`scale(${1})`);
  };

  const onPointerOutEvent = () => {
    setInnerTransformStyle(`scale(${0.6})`);
  };
  
  return (
    <div className="parent">
      <div className="element" style={{transform: innerTransformStyle}} onPointerOut={onPointerOutEvent} onPointerOver={onPointOverEvent}></div>
    </div>
  );
}

ReactDOM.render(<MyComponent/>, document.getElementById("app"));

.parent {
  width: 100px;
  height: 100px;
  background-color: #f00;
}

.element {
  width: 100px;
  height: 100px;
  background-color: #0f0;
  transition: transform 1s;
}

<script src="https://unpkg.com/react@16/umd/react.development.js" crossorigin></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js" crossorigin></script>

<div id="app"></div>

answered Feb 4, 2020 at 0:31

Soc

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2 Comments

Comum Over a year ago

I've implemented this solution and it indeed does work. However because I have two animations that need to work in inverse scale (hence the bit elementScale += (targetScale - elementScale) * easing; innerScale = 1 / elementScale;), a more css oriented solution gives a bit of a wobbly effect (even though I prefere it, as no infinite loops are required). The example I'm trying to convert to react from vanilla was smooth all the way.

Soc Over a year ago

Can you include an executable demo of the wobbly animation?

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