Re: Mixing Elemental2 with GWT Widgets

What I don't understand is why onload and onerror need a return value?  I just return null as I've no clue what the return value should be.

Because these on<Event> properties and their functions are defined that way. For example in the old days you could return false in an onclick function to suppress the click default action of the browser. These days it is recommended to always use addEventListener() instead of these event properties and to suppress the default action you call event.preventDefault().

Also in JS a function basically always have some return value, e.g.

function() {

  return;

  return undefined;

  // no return statement at all

}

is all the same and returns undefined. That is why Promises in elemental2 also feel a bit clunky compared to JS. Promises allow you to return a new Promise/thenable in your success/catch callback methods so elemental2 has to define a return type for these callback functions. If you do not want to return a Promise/thenable in JS then you simply do not write a return statement but in Java you now have to write return null.

-- J. 

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