How to declare simple observer with function

[ghost]

Fixes #2404

[ghost]

@arthurevans and/or @TimvdLippe can has sanity-check?

[TimvdLippe]

Overall LGTM. Just a question on a potentially nicer notation of the function declaration, but it is mostly a nit 😛

[TimvdLippe]

I think a lambda reads clearer. Does the following work?

observer(newValue, oldValue) {
  this.toggleClass('highlight', newValue);
}

[ghost]

So this?

observer: 
  function observer(newValue, oldValue) {
    this.toggleClass('highlight', newValue);
  }

Or ...?

[TimvdLippe]

Like this:

static get properties() {
  return {
    active: {
      type: Boolean,
      // Observer method
      observer(newValue, oldValue) {
          this.toggleClass('highlight', newValue);
      }
  }
}

A running example: http://jsbin.com/xisifaboso/edit?html,console,output This is using the "object method shorthand definition" in ES2015: https://developer.mozilla.org/nl/docs/Web/JavaScript/Reference/Functions/Method_definitions

[ghost]

Cool, didn't know that was a thing XD

[TimvdLippe]

Yeah it is fairly new and neatly concise 😄 This PR now LGTM fully!

[ghost]

Great, thanks!