style: code optimization (#372)

* style: code optimization

* revert

* revert

Author: li-jia-nan

src/raf.ts

@@ -8,13 +8,14 @@ if (typeof window !== 'undefined' && 'requestAnimationFrame' in window) {
 }
 
 let rafUUID = 0;
+
 const rafIds = new Map<number, number>();
 
 function cleanup(id: number) {
   rafIds.delete(id);
 }
 
-export default function wrapperRaf(callback: () => void, times = 1): number {
+const wrapperRaf = (callback: () => void, times = 1): number => {
   rafUUID += 1;
   const id = rafUUID;
 
@@ -39,10 +40,12 @@ export default function wrapperRaf(callback: () => void, times = 1): number {
   callRef(times);
 
   return id;
-}
+};
 
 wrapperRaf.cancel = (id: number) => {
   const realId = rafIds.get(id);
   cleanup(realId);
   return caf(realId);
 };
+
+export default wrapperRaf;