Update a wordpress rest api using javascript fetch method - fetch-api

Question

This is the index.php of my plugin where I am registering a custom POST endpoint.
function __construct()
{
add_action('rest_api_init', array($this, 'add_custom_api'));
}
function add_custom_api()
{
register_rest_route('wyr/v1', 'putAns', array(
'methods' => 'POST',
'callback' => array($this, 'putAns')
));
}
But, I want to insert the data inside this endpoint using a fetch post method from javascript.
function putAns($data)
{
return (); // INSERT SOMETHING FROM JAVASCRIPT
}
This is the javascript code that I'm failing with:
async clickHandler(e) {
const response = await fetch("http://localhost/plugdev/wp-json/wyr/v1/putAns", {
method: "POST",
headers: {
'Content-Type': 'application/json',
},
body: JSON.stringify({
title: 'A blog post by DAVID',
body: 'Brilliant post on fetch API',
userId: 1,
})
});
var data1 = await response.json();
console.log(data1)
}
There are a lot of other details missing but this is the general gist of the issue: Onclick of a button, I want to change the value of a a property inside this object. Then, I'll have to catch this request from php and insert it into the database.