Create/use/test assertNotNull

Author: RoyEJohnson

src/app/components/more-fewer/more-fewer.tsx

@@ -4,6 +4,7 @@ import {FontAwesomeIcon} from '@fortawesome/react-fontawesome';
 import {faCaretLeft} from '@fortawesome/free-solid-svg-icons/faCaretLeft';
 import {faCaretRight} from '@fortawesome/free-solid-svg-icons/faCaretRight';
 import $ from '~/helpers/$';
+import {assertNotNull} from '~/helpers/data';
 import {treatSpaceOrEnterAsClick} from '~/helpers/events';
 
 function PseudoButton({onClick, children}: React.PropsWithChildren<{
@@ -49,7 +50,7 @@ export function Paginated({children, perPage=10}: {
     }
     useEffect(() => {
         if (pageChanged) {
-            $.scrollTo(ref.current as HTMLDivElement, 70);
+            $.scrollTo(assertNotNull(ref.current), 70);
         }
     }, [pageChanged]);
 

src/app/helpers/data.tsx

@@ -7,6 +7,13 @@ export function assertDefined<T>(value: T | undefined): T {
     return value;
 }
 
+export function assertNotNull<T>(value: T | null): T {
+    if (value === null) {
+        throw new Error('Value is null');
+    }
+    return value;
+}
+
 export function formatDateForBlog(date: string) {
     if (!date) {
         return null;

test/src/helpers/data.test.tsx

@@ -1,7 +1,7 @@
 import React from 'react';
 import {describe, test, expect} from '@jest/globals';
 import {render, screen} from '@testing-library/preact';
-import {useSet, assertDefined} from '~/helpers/data';
+import {useSet, assertDefined, assertNotNull} from '~/helpers/data';
 
 function Component() {
     const s = useSet([1]);
@@ -34,4 +34,9 @@ describe('helpers/data', () => {
 
         expect(() => assertDefined(foo)).toThrowError();
     });
+    test('assertNotNull throws', () => {
+        const foo = null;
+
+        expect(() => assertNotNull(foo)).toThrowError();
+    });
 });