3. Callback_functions.js

const Todos = (callback)=>{

const request = new XMLHttpRequest();

request.addEventListener('readystatechange',
()=>{
  if(request.readyState===4 && request.status===200){
    callback(undefined,request.responseText)
  }
  else if(request.readyState===4){
    callback('could not fetch data',undefined)
  }
}

)
request.open('GET','https://jsonplaceholder.typicode.com/todos/');
request.send();
}


console.log(1);
console.log(2);


Todos((err,data)=>{
console.log('callback fired');
if(err){
  console.log(err)
}else{
  console.log(data)
}
})

console.log(3);