Add Client.join, show join errors in popup

lib/client.js

@@ -789,6 +789,32 @@ export default class Client extends EventTarget {
 		});
 	}
 
+	join(channel) {
+		let msg = {
+			command: "JOIN",
+			params: [channel],
+		};
+		return this.roundtrip(msg, (msg) => {
+			switch (msg.command) {
+			case irc.ERR_NOSUCHCHANNEL:
+			case irc.ERR_TOOMANYCHANNELS:
+			case irc.ERR_BADCHANNELKEY:
+			case irc.ERR_BANNEDFROMCHAN:
+			case irc.ERR_CHANNELISFULL:
+			case irc.ERR_INVITEONLYCHAN:
+				if (this.cm(msg.params[1]) === this.cm(channel)) {
+					throw new IRCError(msg);
+				}
+				break;
+			case "JOIN":
+				if (this.isMyNick(msg.prefix.name) && this.cm(msg.params[0]) === this.cm(channel)) {
+					return true;
+				}
+				break;
+			}
+		});
+	}
+
 	fetchBatch(msg, batchType) {
 		let batchName = null;
 		let messages = [];