TIL: Promises in Earth Engine

Using evaluate with a callback function is the standard way to handle potential server-side errors in the Earth Engine JS API, e.g. parsing a date:

ee.Date("2012").evaluate(function(result, err) {
  err ? print(err) : print(result);
});

But what if we want to use promises instead? Let’s write a get_promise function that wraps any evaluatable object in a promise:

/**
 * Return a promise that resolves when an object is evaluated.
 */
function get_promise(object) {
  return new Promise(function(resolve, reject) {
    object.evaluate(function(result, err) {
      err ? reject(err) : resolve(result);
    })
  })
}

Now we can evaluate an object to a promise and handle it like any other promise:

get_promise(ee.Date("2012"))
  .then(print)
  .catch(print);

Cool, but the truth is that you’re probably better off sticking with evaluate callbacks, since the Code Editor seems to only partially support promises¹.