AJAX post call stores data twice in my JSON file – Jquery ajax

I stumbled across a problem in my project. I want to build a kind of archive for news articles using node.js. I store the input of a form (all the relevant data) into a JSON file. This is my form (simplified):

<form id="json-form">
<label class="json-form-labels" for="title">title</label>
<input id="json-form-title" type="text" name="title" required>

<label class="json-form-labels" for="date">date</label>
<input id="json-form-date" type="text" name="date" required>        

<label class="json-form-labels" for="author"><author</label>
<input id="json-form-author" type="text" name="author" required>

<label class="json-form-labels" for="topic">topic</label>
<select id="json-form-topic"name="topic">
    <option value="not_specified"></option>
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
    <option value="4">4</option>
    <option value="5">5</option>
</select>

<label class="json-form-labels" for="Link">link</label>
<input id="json-form-link" type="text" name="link" required>

<label class="json-form-labels" for="description">description</label>
<textarea name="" id="json-form-description-textarea" required>    </textarea>  

<label class="json-form-labels" for="content">content</label>
<textarea name="" id="json-form-content-textarea" required></textarea>

<button id="json-form-submit">Submit</button>
</form>

On submit I am using AJAX to send the data:

$(function() {
$(document).on('click', '#json-form-submit', function(e) {
    e.preventDefault();
    $('#json-form-submit').prop('disabled', true);
    var title = document.getElementById('json-form-title').value; 
    var author = document.getElementById('json-form-author').value; 
    var date = document.getElementById('json-form-date').value; 
    var topic = document.getElementById('json-form-topic').value; 
    var articlelink = document.getElementById('json-form-link').value; 
    var description = document.getElementById('json-form-description-textarea').value; 
    var content = document.getElementById('json-form-content-textarea').value; 
    var data = { title: title, author: author, date: date, related: related, articlelink: articlelink, description: description, content: content };
        
    $.ajax({    
        type: "POST",
        url: '/create-article',
        contentType: 'application/json',
        data: JSON.stringify(data),
        success: function() {
            
        },
        error: function() {
            
        }
    });
});         
});

Server-side I am writing the data in my JSON like this:

app.post('/create-article', (req, res) => {
var title = req.body.title;
var date = req.body.date;
var author = req.body.author;
var topic = req.body.topic;
var articlelink = req.body.articlelink;
var description = req.body.description;
var content = req.body.content;

const data = { title: title, author: author, date: date, topic: topic, articlelink: articlelink, description: description, content: content };

const jsonString = fs.readFileSync('./public/files/js/articles.json');
const jsonObject = JSON.parse(jsonString);
jsonObject.push(data);
fs.writeFileSync('./public/files/js/articles.json', JSON.stringify(jsonObject));
})

The problem I’m facing now is that my the new article is written twice into my JSON file instead of once and I have honestly no clue why. Any help would be appreciated!