JSFiddle - React, Tailwind, and code Playground

JavaScript

let counter=0;
async function requests(url) {
  const returnJson = JSON.stringify({count: ++counter});
	const response = await fetch(url, {
  	method: "POST",
  	headers: {
    	"Content-Type": "application/x-www-form-urlencoded; charset=utf-8"
  	},
  	body: 'json='+encodeURIComponent(returnJson)
	})
  
  if (!response.ok) {
  	throw new Error(`Request failed with status ${response.status}`)
  }
		
  return response.json();
}

async function myExtension(){
	const data = await requests('/echo/json');
  console.log('We have made '+data.count+' requests.');
}

myExtension();

// When you're ready to repeat:
//setInterval(myExtension, 5000);