I am new to Selenium, and new to Node.js. I've done the npm installs and put chromedriver and geckodriver in a directory on my PATH. I am on Mac OS X. Running 'node cheese.js', I immediately get:

```
cheese.js:1
(function (exports, require, module, __filename, __dirname) { var driver = new webdriver.Builder().build();

ReferenceError: webdriver is not defined
    at Object.<anonymous> (/Users/bjbarouch/Sites/cheese.js:1:80)
    at Module._compile (module.js:409:26)
    at Object.Module._extensions..js (module.js:416:10)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)
    at Function.Module.runMain (module.js:441:10)
    at startup (node.js:139:18)
    at node.js:974:3

```

For reference, the cheese code is:

```
var driver = new webdriver.Builder().build();
driver.get('http://www.google.com');

var element = driver.findElement(webdriver.By.name('q'));
element.sendKeys('Cheese!');
element.submit();

driver.getTitle().then(function(title) {
    console.log('Page title is: ' + title);
});

driver.wait(function() {
    return driver.getTitle().then(function(title) {
        return title.toLowerCase().lastIndexOf('cheese!', 0) === 0;
    });
}, 3000);

driver.getTitle().then(function(title) {
    console.log('Page title is: ' + title);
});

driver.quit();

```