feat(shared): add invariant util

packages/autocomplete-js/src/utils/getHTMLElement.ts

@@ -1,6 +1,15 @@
+import { invariant } from '@algolia/autocomplete-shared';
+
 export function getHTMLElement(value: string | HTMLElement): HTMLElement {
   if (typeof value === 'string') {
-    return document.querySelector<HTMLElement>(value)!;
+    const element = document.querySelector<HTMLElement>(value)!;
+
+    invariant(
+      element !== null,
+      `The element ${JSON.stringify(value)} is not in the document.`
+    );
+
+    return element;
   }
 
   return value;

packages/autocomplete-shared/src/index.ts

@@ -1,5 +1,6 @@
 export * from './createRef';
 export * from './debounce';
+export * from './invariant';
 export * from './isEqual';
 export * from './MaybePromise';
 export * from './warn';

packages/autocomplete-shared/src/invariant.ts

@@ -0,0 +1,14 @@
+/**
+ * Throws an error if the condition is not met in development monde.
+ * This is used to make development a better experience to provide guidance as
+ * to where the error comes from.
+ */
+export function invariant(condition: boolean, message: string) {
+  if (!__DEV__) {
+    return;
+  }
+
+  if (!condition) {
+    throw new Error(`[Autocomplete] ${message}`);
+  }
+}