feat: add typeguards to webhooks

src/structures/Webhook.js

@@ -395,6 +395,22 @@ class Webhook {
     return this.client.rest.cdn.Avatar(this.id, this.avatar, format, size);
   }
 
+  /**
+   * Whether or not this webhook is a channel follower webhook.
+   * @returns {boolean}
+   */
+  isChannelFollower() {
+    return this.type === WebhookTypes['Channel Follower'];
+  }
+
+  /**
+   * Whether or not this webhook is an incoming webhook.
+   * @returns {boolean}
+   */
+  isIncoming() {
+    return this.type === WebhookTypes.Incoming;
+  }
+
   static applyToClass(structure, ignore = []) {
     for (const prop of [
       'send',

typings/index.d.ts

@@ -2218,6 +2218,11 @@ export class Webhook extends WebhookMixin() {
   public sourceChannel: NewsChannel | APIPartialChannel | null;
   public token: string | null;
   public type: WebhookType;
+  public isIncoming(): this is this & { token: string };
+  public isChannelFollower(): this is this & {
+    sourceGuild: Guild | APIPartialGuild;
+    sourceChannel: NewsChannel | APIPartialChannel;
+  };
 }
 
 export class WebhookClient extends WebhookMixin(BaseClient) {

typings/tests.ts

@@ -1,8 +1,10 @@
 import {
   APIGuildMember,
-  APIInteractionDataResolvedGuildMember,
   APIInteractionGuildMember,
   APIMessage,
+  APIPartialChannel,
+  APIPartialGuild,
+  APIInteractionDataResolvedGuildMember,
 } from 'discord-api-types/v9';
 import {
   ApplicationCommand,
@@ -478,7 +480,7 @@ client.on('messageReactionRemoveAll', async message => {
 // This is to check that stuff is the right type
 declare const assertIsMessage: (m: Promise<Message>) => void;
 
-client.on('messageCreate', message => {
+client.on('messageCreate', async message => {
   const { channel } = message;
   assertIsMessage(channel.send('string'));
   assertIsMessage(channel.send({}));
@@ -573,6 +575,22 @@ client.on('messageCreate', message => {
     },
   });
 
+  const webhook = await message.fetchWebhook();
+
+  if (webhook.isChannelFollower()) {
+    assertType<Guild | APIPartialGuild>(webhook.sourceGuild);
+    assertType<NewsChannel | APIPartialChannel>(webhook.sourceChannel);
+  } else if (webhook.isIncoming()) {
+    assertType<string>(webhook.token);
+  }
+
+  // @ts-expect-error
+  assertType<Guild | APIPartialGuild>(webhook.sourceGuild);
+  // @ts-expect-error
+  assertType<NewsChannel | APIPartialChannel>(webhook.sourceChannel);
+  // @ts-expect-error
+  assertType<string>(webhook.token);
+
   channel.awaitMessageComponent({
     filter: i => {
       assertType<MessageComponentInteraction>(i);