index.js

var inquirer 	= require("inquirer");
var Client 		= require('node-rest-client').Client;
var client 		= new Client();
var twitchers = ["ESL_SC2", "OgamingSC2", "cretetion", "freecodecamp", "storbeck", "habathcx", "RobotCaleb", "noobs2ninjas"];
console.log("A list of twitch users you can check");
for (var i = 0; i < twitchers.length; i++) {
	console.log(twitchers[i]);
}

function getData (callback){
	var question = [{
		name : 'username',
		type : 'input',
		message: 'Enter a valid twitch username: ',
		validate: function(value) {
			if (value.length) {
				return true;
			} else {
				return 'Please enter a twitch username';
			}
			
		}
	}];
	inquirer.prompt(question).then(callback);
};

function getTwitcher() {
	var username = arguments[0]['username'];
	client.get("https://api.twitch.tv/kraken/streams/"+username+"?client_id=f9b1doaq2gxch1fktp5f76zw2uq8wbu", function (data, response) {
		if (data.stream !== null) {
			if(!data.error) {
				console.log("Name: "+data.stream.channel['display_name']);
				console.log("ID: "+data.stream._id);
				console.log("Game: "+data.stream.game);
				console.log("Total Viewers: "+data.stream.viewers);
			} else {
				console.log(username+" not found!");
			}
		} else {
			console.log("Oops! "+username+" is not a valid twitch username");
		}
	});
}
getData(getTwitcher);