PHP POST JSON JavaScript Fetch Example 1

post.js

fetch("post.php", {
    method: "post",
    mode: "cors",
    headers: {
      "Content-Type": "application/json"
    },
    body: {data: "data"}
  })
    .then(response => {
      return response.text(); // returns text that can used as html
      //return response.json();  // returns json object
    })
    .then(html => {
      document.querySelector("#html_element").innerHTML = html;
    })
    .then(() => {
     // do something else;
    })
    .catch(function(err) {
      console.log("Failed to fetch page: ", err);
    });

post.php

$data = json_decode(trim(file_get_contents("php://input")));

// do something with $data;