using shouldComponentUpdate instead of getSnapshotBeforeUpdate

Hi, I'm struggling a little with the new lifecycles. I have this component which passes down a style which will lock the scrollbar on the window without shifting content when applied on my root App element.

interface ScrollLockProps {
  locked: boolean,
  children: (style?: CSSProperties) => React.ReactNode
}

export class ScrollLock extends React.Component<ScrollLockProps> {
  private scrollY = 0

  public shouldComponentUpdate() {
    if (!this.props.locked) {
      this.scrollY = window.scrollY
    }

    return true
  }

  public componentDidUpdate() {
    if (!this.props.locked) {
      window.scrollTo(0, this.scrollY)
    }
  }

  public render() {
    const { locked, children } = this.props

    const style: CSSProperties | undefined = locked ? {
      position: "fixed",
      left: "0px",
      right: "0px",
      top: `-${this.scrollY}px`,
    } : undefined

    return children(style)
  }
}

The problem is I have to use shouldComponentUpdate to retrieve the scroll position, and this feels wrong to me as this lifecycle surely should only return a boolean and not have any side effects?

I can't use getSnapshotBeforeUpdate because render is called before it, which means the resulting style will be incorrect.

And of course I cannot use componentWillReceiveProps because it is deprecated.
What is the correct way to go about this?

Das Issue stellt eine Inline-TypeScript-ScrollLock-Komponente bereit, statt Repository-Dateien oder Tests zu benennen. Beginne mit der Überprüfung der React-Lebenszyklusdokumentation zu shouldComponentUpdate, getSnapshotBeforeUpdate und componentDidUpdate; abgeschlossen ist die Aufgabe, wenn der korrekte Lebenszyklusansatz für diesen Fall der Scroll-Sperre festgelegt und dokumentiert ist.