feat(Channel): add isText() type guard (#4745)

src/structures/Channel.js

@@ -97,6 +97,14 @@ class Channel extends Base {
     return this.client.channels.fetch(this.id, true, force);
   }
 
+  /**
+   * Indicates whether this channel is text-based.
+   * @returns {boolean}
+   */
+  isText() {
+    return 'messages' in this;
+  }
+
   static create(client, data, guild) {
     const Structures = require('../util/Structures');
     let channel;

typings/index.d.ts

@@ -187,6 +187,7 @@ declare module 'discord.js' {
     public type: keyof typeof ChannelType;
     public delete(reason?: string): Promise<Channel>;
     public fetch(force?: boolean): Promise<Channel>;
+    public isText(): this is TextChannel | DMChannel | NewsChannel;
     public toString(): string;
   }
 
@@ -826,6 +827,7 @@ declare module 'discord.js' {
       options: PermissionOverwriteOption,
       reason?: string,
     ): Promise<this>;
+    public isText(): this is TextChannel | NewsChannel;
   }
 
   export class GuildEmoji extends BaseGuildEmoji {