refine types for browser event handler

Signed-off-by: eternal-flame-AD <[email protected]>

js/igv.d.ts

@@ -732,19 +732,19 @@ interface CreateOptExtras {
 export namespace BrowserEvents {
     export type EventType = "trackremoved" | "trackdrag" | "trackdragend" | "locuschange" | "trackclick" | "trackorderchanged";
 
-    export type EventPayload<T extends EventType> =
-        T extends "trackremoved" ? Tracks.Track[] :
-        T extends "locusChange" ? {
+    export type EventHandler<T extends EventType> =
+        T extends "trackremoved" ? (tracks: Tracks.Track[]) => EventReturn<T> :
+        T extends "locusChange" ? (loci: {
             chr: string;
             start: number;
             end: number;
             getLocusString: () => string;
-        }[] :
-        T extends "trackclick" ? {
-            name: string;
-            value: string;
-        } :
-        T extends "trackorderchanged" ? string[] :
+        }[]) => EventReturn<T> :
+        T extends "trackclick" ? (
+            track: Tracks.Track,
+            popoverData?: Record<string, string>,
+        ) => EventReturn<T> :
+        T extends "trackorderchanged" ? (trackNames: string[]) => EventReturn<T> :
         never;
 
     export type EventReturn<T extends EventType> =
@@ -816,7 +816,7 @@ declare class _Browser {
 
     sessionURL(): string;
 
-    on<T extends BrowserEvents.EventType>(event: T, handler: (payload: BrowserEvents.EventPayload<T>) => BrowserEvents.EventReturn<T>): void;
+    on<T extends BrowserEvents.EventType>(event: T, handler: BrowserEvents.EventHandler<T>): void;
     off(event: BrowserEvents.EventType): void;
 }