1 files changed, 17 insertions, 0 deletions
diff --git a/packages/frontend-shared/js/url.ts b/packages/frontend-shared/js/url.ts
index eb830b1eea..e4f9ca513d 100644
--- a/packages/frontend-shared/js/url.ts
+++ b/packages/frontend-shared/js/url.ts
@@ -26,3 +26,20 @@ export function extractDomain(url: string) {
 	const match = url.match(/^(?:https?:)?(?:\/\/)?(?:[^@\n]+@)?([^:\/\n]+)/im);
 	return match ? match[1] : null;
 }
+
+export function maybeMakeRelative(urlStr: string, baseStr: string): string {
+	try {
+		const baseObj = new URL(baseStr);
+		const urlObj = new URL(urlStr);
+		/* in all places where maybeMakeRelative is used, baseStr is the
+		 * instance's public URL, which can't have path components, so the
+		 * relative URL will always have the whole path from the urlStr
+		*/
+		if (urlObj.origin === baseObj.origin) {
+			return urlObj.pathname + urlObj.search + urlObj.hash;
+		}
+		return urlStr;
+	} catch (e) {
+		return '';
+	}
+}