client.on error

[Makayla]

Issue Solved

[Rozi Vector]

You need define the client bot first:

const Discord = require('discord.js');
const client = new Discord.Client();

[Eduard]

client variable is assumed to be the variable that defines your new Discord.Client()
If your code is different you literally have to change 1 name in the code you have.
Therefore this issue is irrelevant.