2 files changed, 15 insertions, 0 deletions

diff --git a/source/helpers/types.d.ts b/source/helpers/types.d.ts
index 06f4cb80..e3224b49 100644
--- a/source/helpers/types.d.ts
+++ b/source/helpers/types.d.ts
@@ -15,4 +15,9 @@ declare global {
 		closest<S extends string>(selector: S | readonly S[]): StrictlyParseSelector<S, HTMLElement> | null;
 		matches(selectors: string | readonly string[]): boolean;
 	}
+
+	// This cannot be a regular import because it turns `globals.d.ts` in a "module definition", which it isn't
+	type Browser = import('webextension-polyfill').Browser;
+	const browser: Browser;
+
 }
diff --git a/source/helpers/used-storage.ts b/source/helpers/used-storage.ts
new file mode 100644
index 00000000..8a95bf18
--- /dev/null
+++ b/source/helpers/used-storage.ts
@@ -0,0 +1,10 @@
+/** `getBytesInUse` polyfill */
+export default async function getStorageBytesInUse(area: 'local' | 'sync'): Promise<any> {
+	const storage = browser.storage[area];
+	// From https://bugzilla.mozilla.org/show_bug.cgi?id=1385832#c20
+	return 'getBytesInUse' in storage ? storage.getBytesInUse() : new TextEncoder().encode(
+		Object.entries(await storage.get())
+			.map(([key, value]) => key + JSON.stringify(value))
+			.join(''),
+	).length;
+}