JSFiddle - React, Tailwind, and code Playground

JavaScript

var myjson = [{
  "firstName": "John",
  "lastName": "Doe"
}, {
  "firstName": "Anna",
  "lastName": "Smith"
}, {
  "firstName": "Peter",
  "lastName": "Jones"
}];

var keys = [];
for(let key in myjson[0]) keys.push(key);

var tbl = "<table>"

$.each(myjson, function() {
  tbl += "<tr>";
  for(let index in keys) tbl += '<td>' + keys[index] + '</td>';
  tbl += "</tr>";
  tbl += "<tr>";
  for(let index in keys) tbl += '<td>' + arguments[1][keys[index]] + '</td>';
  tbl += "</tr>";
});

tbl += "</table>";

document.body.innerHTML = tbl;