Cannot read property 'add' of undifined, Discord add role - discord

Question

So I decided to start making a very simple Discord bot that should give a role to a member if a different member has the same role,
For example;
Person 1: I have the infected role
Person 2: I dont have the infected role.
Person 2: #Person1 blah blah blah
And now person 2 should receive the infected role, Instead that doesn't happen, And I cannot figure out a way to fix it.
const Discord = require('discord.js');
const client = new Discord.Client();
client.on('ready', () => {
console.log(`Logged in as ${client.user.tag}!`);
console.log("rerararararrederasd")
var infectionStarted = true; client.on("message", message => {
if (infectionStarted) {
try{ let role = message.guild.roles.cache.find(r => r.name === 'infected');
client.users.cache.get(message.mentions.members.first().id).roles.add(role);}catch(e){console.log(e)};
}
});
client.login('my discord bots token ofc goes here i just removed for stackoverflow');
But in the console I get this issue report:
at Client.emit (events.js:196:13)
at MessageCreateAction.handle (/rbd/pnpm-volume/ec7e49f1-7b76-4ef8-9653-1982138496c7/node_modules/.registry.npmjs.org/discord.js/12.3.1/node_modules/discord.js/src/client/actions/MessageCreate.js:31:14)
at Object.module.exports [as MESSAGE_CREATE] (/rbd/pnpm-volume/ec7e49f1-7b76-4ef8-9653-1982138496c7/node_modules/.registry.npmjs.org/discord.js/12.3.1/node_modules/discord.js/src/client/websocket/handlers/MESSAGE_CREATE.js:4:32)
at WebSocketManager.handlePacket (/rbd/pnpm-volume/ec7e49f1-7b76-4ef8-9653-1982138496c7/node_modules/.registry.npmjs.org/discord.js/12.3.1/node_modules/discord.js/src/client/websocket/WebSocketManager.js:384:31)
at WebSocketShard.onPacket (/rbd/pnpm-volume/ec7e49f1-7b76-4ef8-9653-1982138496c7/node_modules/.registry.npmjs.org/discord.js/12.3.1/node_modules/discord.js/src/client/websocket/WebSocketShard.js:444:22)
at WebSocketShard.onMessage (/rbd/pnpm-volume/ec7e49f1-7b76-4ef8-9653-1982138496c7/node_modules/.registry.npmjs.org/discord.js/12.3.1/node_modules/discord.js/src/client/websocket/WebSocketShard.js:301:10)
at WebSocket.onMessage (/rbd/pnpm-volume/ec7e49f1-7b76-4ef8-9653-1982138496c7/node_modules/.registry.npmjs.org/ws/7.3.1/node_modules/ws/lib/event-target.js:125:16)
at WebSocket.emit (events.js:196:13)
at Receiver.receiverOnMessage (/rbd/pnpm-volume/ec7e49f1-7b76-4ef8-9653-1982138496c7/node_modules/.registry.npmjs.org/ws/7.3.1/node_modules/ws/lib/websocket.js:797:20)
TypeError: Cannot read property 'add' of undefined
It might be very obvious but i dont know how to solve this, If you could help me i would really appreciate it, Thank you!

Answer 1

EDIT:
I recommend structuring your code a little better as well as destructuring your variables.
The issue is that client.users.fetch() returns a user which unlike a member has no roles. Hence why it returned undefined
client.on("message", message => {
const infectionStarted = true
const role = message.guild.roles.cache.find(r => r.name === 'infected')
// have 'member' = the mentioned member
const member = message.mentions.members.first()
// If there was a mention, add the role to the mentioned
if (member) {
// Instead of fetching the user through Discord, I add the role directly to the member object like this
member.roles.cache.add(role)
}
}