type Relay EventHandler (#121)

* type Relay EventHandler

* Update relay.ts

relay.ts

@@ -4,7 +4,12 @@ import {Event, verifySignature, validateEvent} from './event'
 import {Filter, matchFilters} from './filter'
 import {getHex64, getSubscriptionId} from './fakejson'
 
-type RelayEvent = 'connect' | 'disconnect' | 'error' | 'notice'
+type RelayEvent = {
+	connect: () => void
+	disconnect: () => void
+	error: () => void
+	notice: (msg: string) => void
+}
 
 export type Relay = {
   url: string
@@ -15,8 +20,8 @@ export type Relay = {
   list: (filters: Filter[], opts?: SubscriptionOptions) => Promise<Event[]>
   get: (filter: Filter, opts?: SubscriptionOptions) => Promise<Event | null>
   publish: (event: Event) => Pub
-  on: (type: RelayEvent, cb: any) => void
-  off: (type: RelayEvent, cb: any) => void
+  off: <T extends keyof RelayEvent, U extends RelayEvent[T]>(event: T, listener: U) => void
+  on: <T extends keyof RelayEvent, U extends RelayEvent[T]>(event: T, listener: U) => void
 }
 export type Pub = {
   on: (type: 'ok' | 'failed', cb: any) => void
@@ -46,12 +51,7 @@ export function relayInit(
 
   var ws: WebSocket
   var openSubs: {[id: string]: {filters: Filter[]} & SubscriptionOptions} = {}
-  var listeners: {
-    connect: Array<() => void>
-    disconnect: Array<() => void>
-    error: Array<() => void>
-    notice: Array<(msg: string) => void>
-  } = {
+  var listeners: { [TK in keyof RelayEvent]: RelayEvent[TK][]} = {
     connect: [],
     disconnect: [],
     error: [],
@@ -242,14 +242,15 @@ export function relayInit(
 
   return {
     url,
-    sub,
-    on: (type: RelayEvent, cb: any): void => {
-      listeners[type].push(cb)
-      if (type === 'connect' && ws?.readyState === 1) {
-        cb()
-      }
-    },
-    off: (type: RelayEvent, cb: any): void => {
+	sub,
+	on: <T extends keyof RelayEvent, U extends RelayEvent[T]>(type: T, cb: U): void => {
+		listeners[type].push(cb)
+		if (type === 'connect' && ws?.readyState === 1) {
+			// i would love to know why we need this
+			(cb as ()=> void)()
+		}
+	},
+	off: <T extends keyof RelayEvent, U extends RelayEvent[T]>(type: T, cb: U): void => {
       let index = listeners[type].indexOf(cb)
       if (index !== -1) listeners[type].splice(index, 1)
     },