discord.js v12 roles size guild code example
Example: get discord.js role
let role = message.guild.roles.cache.find(r => r.id === "Role ID");
// The member you want to add the role to
let member = message.mentions.members.first();
// Add role to the member
member.roles.add(role);
// Or add it to yourself
message.author.roles.add(role);