impl #81 custom event

This is the record side impl of custom event, according to the
issue, we may also add first-class support for the custom event
tag like display color labels in the replayer-ui.

src/record/index.ts

@@ -17,6 +17,23 @@ function wrapEvent(e: event): eventWithTime {
   };
 }
 
+let wrappedEmit!: (e: eventWithTime, isCheckout?: boolean) => void;
+
+export function addCustomEvent<T>(tag: string, payload: T) {
+  if (!wrappedEmit) {
+    throw new Error('please add custom event after start recording');
+  }
+  wrappedEmit(
+    wrapEvent({
+      type: EventType.Custom,
+      data: {
+        tag,
+        payload,
+      },
+    }),
+  );
+}
+
 function record(options: recordOptions = {}): listenerHandler | undefined {
   const {
     emit,
@@ -34,7 +51,7 @@ function record(options: recordOptions = {}): listenerHandler | undefined {
 
   let lastFullSnapshotEvent: eventWithTime;
   let incrementalSnapshotCount = 0;
-  const wrappedEmit = (e: eventWithTime, isCheckout?: boolean) => {
+  wrappedEmit = (e: eventWithTime, isCheckout?: boolean) => {
     emit(e, isCheckout);
     if (e.type === EventType.FullSnapshot) {
       lastFullSnapshotEvent = e;