Fetch Example

fetchData.js

// I find MDN have the best resources for most JS stuff: https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API
// using async/await
(async function() {
  // when using await, the function in the outer scope must be declared `async` otherwise it won't work and
  // you'll get very mysterious error messages
  try {
    const response = await fetch('some/url');
    // response.ok is generally a status code between 200 & 299
    if (response.ok) {
      let data;
      if (response.headers.get('content-type') === 'application/json') {
         // this is a convenience function that basically calls JSON.parse() on response.text(), 
         // so it saves you an extra step
         data = await response.json();
      } else {
         data = await response.text(); 
      }
      console.log('Your data should be here', data);
    } catch (err) {
      console.error('remember to always deal with your errors!', err);
    }
})();


// using promises
fetch(‘/some/url’)
  .then(function(response) {
    if (response.ok) {
      if (response.headers.get('content-type') === 'application.json') {
         // this returns a new promise so you need a new `.then()` to get the value
         return response.json();
      } else {
         // as above this returns a new promise
         return response.text();
      }
    }
  })
  .then(function(data) {
    console.log('This should be the data you are expecting', data);
  })
  .catch(function(error) {
    console.error('remember to always deal with your errors!', error);
  });