Edit in JSFiddle

const settings = {
  service: {
    apiKey:       "E8FEF7AE-3F36-4EAF-A451-456D05E6F2A3",
    serviceUrl:   '//rtg.prowritingaid.com'
  },
  grammar: {
    languageFilter:   null,
    languageIsoCode:  null,
    checkStyle:       true,
    checkSpelling:    true,
    checkGrammar:     true,
    checkerIsEnabled: true
  }
};
const GrammarChecker = window["BeyondGrammar"]["GrammarChecker"];
const $textarea = document.querySelector('textarea');
const checker = new GrammarChecker($textarea, settings.service, settings.grammar);

checker.init()
.then(() => checker.activate())

<script src="//cdn.prowritingaid.com/beyondgrammar/2.0.2893/dist/hayt/bundle.js"></script>

<div class="wrapper">
<textarea>
Novalk Djokovic is set to miss the US Open after one of his doctors made an announcement that he will need six to twelve weeks to recovers from a elbow injury.

But Andy Murrey's chances of playing at Flushing Meadows would appear more positive, with the Scot continuing his rehabilitation from a hip problem.

The last grandslam of the year starts in just under five weeks on August 28, meaning Djokovic will run out of time if the latest assessment is correct.

Injured Djokovic starting to consider a break away from tennis. The 12-time major champion was forced to retire injured during his Wimbeldon quarter-final against Tomas Berdych earlier this month and said after the match that he had been feeling pain in his right elbow for over a year and a half. According to his physio its not doing very well. If he does return he will be more likely to injure it again.

He has since been seeking advice from specialists, including Serbian doctor Zdenko Milinkovic, who said Djokovic is suffering from a "bruised bone due to excessive playing".

"Nole must rest for six to 12 weeks," Milinkovic told Sportski Zurnal, a sports newspaper in Serbia.

The next examination will know wether this asdsessment stays or changes. During this period, he is not going to train with a racket but he will run other sessions, such as fitness and the like.
</textarea>
</div>

.wrapper {
  position: fixed;
  top: 10px;
  left: 10px;
  right: 10px;
  bottom: 10px;
}

textarea {
  width: 100%;
  height: 75%;
}