JSFiddle - React, Tailwind, and code Playground

HTML

<form action="">
  <input type="text" name="name"><br>
  <input type="text" name="nature"><br>
  <input type="text" name="age"><br>
</form>

JavaScript

// object with data
let data = {
	name: 'Vasya',
  nature: 'Competitor',
  age: 12
}

// load data to form
for (let fieldName in data) {
  let input = document.querySelector('input[name='+fieldName+']')
  input.value = data[fieldName]
}

// serialize form
let form = document.querySelector('form')
let serialized = new FormData(form) // send it with AJAX

console.log(...serialized)