what software does discord.js guide use code example

Example: Discord.js Basics

const Discord = require("discord.js")
const client = new Discord.Client()
client.on("ready", ()=>{
console.log(`Logged in as ${client.user.tag}`)
})
client.on("message", async function (message) {
  if(message.content === "!test") {
	message.reply("Hello World!")
  }
})