The type 'HTMLDivElement | null' cannot be assigned to the type 'HTMLDivElement' in this context

Struggling with a scroll function to maintain position while scrolling up or down - encountering an error:

Error: Type 'HTMLDivElement | null' is not assignable to type 'HTMLDivElement'.
Type 'null' is not assignable to type 'HTMLDivElement'.ts(2322)

If anyone can assist in fixing this issue, it would be greatly appreciated!

scrollFunction = (): void => {
  if (this.isLargerScreenMedia()) {
        // some code here
  } else {
    const scrollPosition: number = document.documentElement.scrollTop;
    const container: HTMLDivElement =
      this.tripTotalContainer.querySelector('.trip-total-module');
    if (container) {
      if (scrollPosition > this.lastScrollPosition) {
        //scrolling down
        container.style.bottom = '0px';
      } else {
        //scrolling up
        container.style.bottom = '27px';
      }
    }
    this.lastScrollPosition = scrollPosition < 0 ? 0 : scrollPosition;
    this.tripTotalContainer.classList.add('sticky-bottom');
  }
};

Answer №1

When using the querySelector method, keep in mind that its return type is either Element or null. If no matching element is found, it will return null.

The error you're experiencing is likely due to assuming that totalCon is of type

HTMLDivElement</code without accounting for the possibility of <code>null
:

const totalCon: HTMLDivElement = this.tripTotalContainer.querySelector('.trip-total-module');

Your code already seems to handle cases where totalCon could be falsy, so you could simply remove the explicit type declaration:

const totalCon = this.tripTotalContainer.querySelector('.trip-total-module');

Alternatively, you can adjust the explicit type declaration to include null as a possible type:

const totalCon: HTMLDivElement | null = this.tripTotalContainer.querySelector('.trip-total-module');

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