[misc] add typings for duration.isValid() (#4681)

diff --git a/moment.d.ts b/moment.d.ts
index 3256e2b853cab7b0b9dadb3bc5aa8ff930b1b3f6..55a9d1f98bf2827f00211c4d03ee2236d1e42627 100644 (file)
--- a/moment.d.ts
+++ b/moment.d.ts
@@ -197,6 +197,8 @@ declare namespace moment {
 
     toISOString(): string;
     toJSON(): string;
+    
+    isValid(): boolean;
 
     /**
      * @deprecated since version 2.8.0