Simple snippet that set bot banner to gif

index.js

const { REST } = require('@discordjs/rest');
const { readFileSync } = require('fs');

const client = new REST({ version: '9' }).setToken('BOTTOKEN');

const banner = readFileSync('./file.gif');

client.patch('/users/@me', {
	body: {
		banner: `data:image/gif;base64,${banner.toString('base64')}`,
	},
});