What factors does React consider when deciding between replacing or updating a component?

Question

What factors does React consider when deciding between replacing or updating a component?

This particular snippet of code showcases a function called Baz:

function Baz({on}) {
  const rect1 = <rect x='10' y='10' fill='red' width='10' height='10' />
  const rect2 = <rect x='80' y='10' fill='red' width='10' height='10' />
  const Rect3 = () => <rect x='10' y='80' fill='red' width='10' height='10' />
  const Rect4 = () => <rect x='80' y='80' fill='red' width='10' height='10' />
  return (
    <svg viewBox="0 0 100 100">
      { on ? rect1 : rect2 }
      { on ? <Rect3 /> : <Rect4 /> }
    </svg>
  );
}

One interesting behavior here is that the transition from rect1 to rect2 will animate (if css transitions are enabled), while the transition from Rect3 to Rect4 won't.

The question arises: Why does this happen, and are there any potential workarounds?

To better understand this concept, feel free to check out this interactive example on jsfiddle: https://jsfiddle.net/2jLtn39z/

html css reactjs animation svg

Answer 1

Answer №1

It seems like the initial update happens when you make modifications to the jsx elements in the first scenario, while in the second scenario, the component gets swapped out for a different one.

Answer 2

It seems like the initial update happens when you make modifications to the jsx elements in the first scenario, while in the second scenario, the component gets swapped out for a different one.

Answer 3

Answer №2

After receiving some great advice, I was able to find a solution that worked for me. By changing the <Rect3 /> element (which mounts Rect3 as a Component) to { Rect3() } (which returns the JSX elements and inserts them into the parent component without creating new components), I was able to make the animation work smoothly. This technique also applies to SVGs imported as ReactComponents, but keep in mind that if the imported SVG is a class-component rather than a functional component, you will need to call its render method instead.

If you're interested, here's an updated fiddle with the solution: https://jsfiddle.net/Ld6e0zyj/

const useState = React.useState
function Svg() {
  const [on, setOn] = useState(true);
  const toggle = () => setOn(on => !on);
  const rect1 = <rect x='10' y='10' fill='red' width='10' height='10' />;
  const rect2 = <rect x='80' y='10' fill='red' width='10' height='10' />;
  const Rect3 = () => <rect x='10' y='80' fill='red' width='10' height='10' />;
  class Rect4 extends React.Component {
    render() {
      return <rect x='80' y='80' fill='red' width='10' height='10' />;
    }
  }
  return (
    <div>
      <svg viewBox="0 0 100 100">
        { on ? rect1 : rect2 }
        { on ? Rect3() : new Rect4().render() }
      </svg>
      <button onClick={toggle}> Toggle </button>
    </div>
  );
}
ReactDOM.render(<Svg />, document.querySelector("#app"))

Answer 4

After receiving some great advice, I was able to find a solution that worked for me. By changing the <Rect3 /> element (which mounts Rect3 as a Component) to { Rect3() } (which returns the JSX elements and inserts them into the parent component without creating new components), I was able to make the animation work smoothly. This technique also applies to SVGs imported as ReactComponents, but keep in mind that if the imported SVG is a class-component rather than a functional component, you will need to call its render method instead.

If you're interested, here's an updated fiddle with the solution: https://jsfiddle.net/Ld6e0zyj/

const useState = React.useState
function Svg() {
  const [on, setOn] = useState(true);
  const toggle = () => setOn(on => !on);
  const rect1 = <rect x='10' y='10' fill='red' width='10' height='10' />;
  const rect2 = <rect x='80' y='10' fill='red' width='10' height='10' />;
  const Rect3 = () => <rect x='10' y='80' fill='red' width='10' height='10' />;
  class Rect4 extends React.Component {
    render() {
      return <rect x='80' y='80' fill='red' width='10' height='10' />;
    }
  }
  return (
    <div>
      <svg viewBox="0 0 100 100">
        { on ? rect1 : rect2 }
        { on ? Rect3() : new Rect4().render() }
      </svg>
      <button onClick={toggle}> Toggle </button>
    </div>
  );
}
ReactDOM.render(<Svg />, document.querySelector("#app"))

What factors does React consider when deciding between replacing or updating a component?

Answer №1

Answer №2

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