JSON.parse() Vs. .json()

Question

I have been working with fetch API and Promises recently and I came across .json() . Oftentimes .json() returns the same output as JSON.parse. I googled the question and the results pointed in other directions.

Example with XHR and JSON.parse:

$('#xhr').click(function(){
  var XHR = new XMLHttpRequest();

  XHR.onreadystatechange = function(){
    if (XHR.status == 200 && XHR.readyState == 4) {
      $('#quote').text(JSON.parse(XHR.responseText)[0]);
    }
  };

  XHR.open("GET", url);
  XHR.send();
});

Example with Fetch API:

$('#fetch').click(function(){
  fetch(url)
  .then(function(res){
    return res.json();
  })
  .then(function(quote){
    $('#quote').text(quote);
  })
  .catch(function(err){
    handleError(err);
  });
});

Could someone please explain the difference between these seemingly similar concepts ? Thanks

Answer 1

Body.json() is asynchronous and returns a Promise object that resolves to a JavaScript object. JSON.parse() is synchronous can parse a string and change the resulting returned JavaScript object.

Answer 2

'AJAX' works with 'callbacks'; 'fetch' works with 'promises'.

Use JSON.parse() to parse the response for AJAX. Use json() to parse the response for fetch.