demo.html

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8"> 
        <script>
            function hit(passage, question){
                var xhr = new XMLHttpRequest();
                xhr.open("POST", '/answer', true);
                xhr.setRequestHeader("Content-type", "application/json");
                xhr.onreadystatechange = function () {
                    console.log(xhr.status);
                    if (xhr.readyState === 4 && xhr.status === 200) {
                        var json = JSON.parse(xhr.responseText);
                        console.log(json.answer);
                        var ans = document.getElementById("answer");
                        ans.innerHTML = json.answer;
                    }
                };
                var params = JSON.stringify({"question": question, "passage": passage});
                xhr.send(params);
                console.log("sent");
            }
        </script>
        <style>
            body{
                display: grid;
                grid-template-columns: 7fr 3fr;
                grid-template-rows: 9fr 1fr;
            }
        </style>
    </head>
    <body>
        <textarea id='passage' placeholder='Your passage here'></textarea>
        <textarea id='question' placeholder='Your Question here'></textarea>
        <p id='answer'>Your answer appears here</p>
        <button id='GetAnswer'>Get Answer</button>
        <script>
            var button = document.getElementById("GetAnswer");
            button.onclick = function (){
                var para = document.getElementById("passage");
                var ques = document.getElementById("question");
                console.log("hitting");
                hit(para.value, ques.value);

            };
        </script>
    </body>
</html>