我正在尝试使用ntwitter在putty终端上显示一些tweet。在根目录中安装了节点模块(express和ntwitter)，当我尝试从根目录运行tweet_counter.js时，我得到了这个错误。

vagrant@precise32:~/app/Twitter$ node tweet_counter
/home/vagrant/app/Twitter/tweet_counter.js:7
twitter.stream(
    ^
TypeError: Cannot call method 'stream' of undefined
at Object.<anonymous> (/home/vagrant/app/Twitter/tweet_counter.js:7:9)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)
at node.js:906:3

var ntwitter = require("ntwitter"),
credentials = require("./credentials.json"),
twitter;
// set up our twitter object
twitter = ntwitter(credentials);
// set up our twitter stream with three parameters,
// separated by commas
twitter.stream(
// the first parameter is a string
"statuses/filter",
// second parameter, an object containing an array
{ "track": ["awesome", "cool", "rad", "gnarly", "groovy"] },
// the third parameter is our callback for when the stream is created
    function(stream) {
        stream.on("data", function(tweet) {
             console.log(tweet.text);
        });
    }
);