Possible Unhandled Promise Rejection. Cannot read property of undefined

Question

I am new to functional Javascript and promises. The code bellow works great until I uncomment this.writeDataToRealm(data.data). Then I get this error:

Pos

Answer 1

The unhandled rejection is because you forgot to return the inner promise from the then callback, which causes an exception not to bubble to your catch handler:

.then(function(response) {
  if (response.status !== 200) {
    console.log('Error Status Code: ' + response.status);
    // you might want to `throw` here
  } else {
    return response.json().then(function(data) {
      console.log(data);
      return data.data;
    })
  }
});

---

The problem with Cannot read property 'writeDataToRealm' of undefined is caused by this not being the instance you expected - see How to access the correct this / context inside a callback?. The simplest solution would be using an arrow function for the callback.

…
.then(data => {
  this.writeDataToRealm(data)
}, err => {
  console.log('Fetch Error: ', err);
});