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?

The issue provides an inline TypeScript ScrollLock component rather than naming repository files or tests. Start by reviewing the React lifecycle documentation for shouldComponentUpdate, getSnapshotBeforeUpdate, and componentDidUpdate; done means establishing and documenting the correct lifecycle approach for this scroll-locking case.