http://stackoverflow.com/questions/22202421/undefined-callback-in-function

gistfile1.js

var fs = require('fs');

function isPlayerBanned(name,isbanned) {
	fs.readFile('bans.json', 'utf8', function (err,data) {
	    if (err) {
	        console.log(err);
	    }

	    var retorna;

	    var banFile = {};
	    var isBanned = true;
	    if ( banFile[name] !== undefined ) {
	        isBanned = true;
	    }
	    if (isBanned){
	        var banExpiration = banFile[name];
	        var actualTime = new Date();
	        var banDate = new Date(banExpiration);
	        var timeban = banDate.getTime();
	        var time = actualTime.getTime();
	        if (time > timeban){
	            console.log("oi");
	            retorna =  false;
	        } else {
	            console.log("falhou denovo :(");
	            retorna =  true;
	        }
	    } else {
	        console.log('fail 2');
	        retorna =  false;
	    }
	    return isbanned(retorna);
	});
}

isPlayerBanned('name', function(banned) {
	console.log(banned);
	if (banned){
    	console.log(": You can't add because you are banned. Use !isbanned [yourauthname] to know when the ban will expire.");
	}
});