title: Nightwatch.js get value from input and use it in next step
body: <p>I'm trying to run Nightwatch script which will open a url, then it will getValue from an Input and will use that value in the next page.</p>
  
  <p>Please see the following code:</p>
  
  <pre><code>var conf = require('../../nightwatch.conf.BASIC.js');
  
  module.exports = {
      'nightwatch flow': function (browser) {
          var first_name;
          browser
              .url('http://example:3000')
              .getValue('input[name="first_name"]', function(result){
                  first_name = result.value;
              })
              .setValue('input[name="amount"]', 101)
              .click('input[name=continue]')
              .clearValue('input[name="first_name"]')
              .setValue('input[name="first_name"]', first_name)
              .click('button[name=next]')
              .end();
      }
  };
  </code></pre>
  
  <p>the <code>setValue('input[name="first_name"]', first_name)</code>
  gets "undefined"</p>
  
  <p>first_name parameter is being updated inside a callback function.
  I need that setValue function will use the updated value.
  Thanks in advance</p>