JSFiddle - React, Tailwind, and code Playground

JavaScript

function functionOne(_callback){
      let fetchRes = fetch(
    "https://jsonplaceholder.typicode.com/todos/1");
  fetchRes.then(res =>
    res.json()).then(d => {
    console.log(d)
  })
    _callback();
}

function functionTwo(){
    // do some asynchronus work 
    functionOne(()=>{
        console.log("I am a callback, I should come last");
    });
}

functionTwo();