How to find a user by username discord.js code example

Example 1: discord.js get user by id

client.users.cache.find(user => user.id === 'USER-ID')

Example 2: check user by id discord js

if(!message.author.id ==`329023088517971969` || !message.member.hasPermission(['MANAGE_GUILD'])) return message.channel.send(`You don't have the permissions to do this!`)
<code here>