I test ES6 Promise in react APP, but i've not result on my .then :

```
function addItem (value) {
  return new Promise((resolve, reject) => {
    document.getElementById('todo').innerHTML += `<li>${value}</li>`;
  });
}

addItem(value).then(() => {
  alert('then !');
}).catch((err) => {
  console.log(err)
})

```

My function is executed, but i've not event on my then.

Do you know where i was wrong ? Thank you ! :)