feat(ElementEvents): batch subscription

[bigopon]

This PR enhance ElementEvents class with ability to subscribe to multiple events at once.

Usage example:

  import { ElementEvents } from 'aurelia-framework'

  const input = document.createElement('input');
  const elementEvents = new ElementEvents(input);
  elementEvents.subscribe({
    input: () => {
        // handle input value changed
    },
    blur: () => {
        // handle input blur
    },
    focus: {
      handler: () => {
        // handle input focus
      },
      once: true
    }
  });

Also compatible with subscribeOnce

  import { ElementEvents } from 'aurelia-framework'

  const input = document.createElement('input');
  const elementEvents = new ElementEvents(input);
  elementEvents.subscribeOnce({
    input: () => {
        // handle input value changed
    },
    blur: () => {
        // handle input blur
    },
    focus: {
      handler: () => {
        // handle input focus
      },
      once: false
    },
    keydown: {
      handler: () => {},
      once: true,
      capture: true
    }
  });

The result of subscribe / subscribeOnce will be an plain object with same properties with input:

  import { ElementEvents } from 'aurelia-framework'

  const input = document.createElement('input');
  const elementEvents = new ElementEvents(input);
  const subscriptions = elementEvents.subscribe({
    input: () => { },
    blur: () => { },
    focus: {
      handler: () => { },
      once: false
    }
  });

  Object.keys(subscriptions); // <======= ['input', 'blur', 'focus']

  // To dispose single
  subscriptions.input.dispose();

[bigopon]

If this gets merged, then it should be encouraged over the other overload signature with traditional arguments:

subscribe(
  eventName: string,
  handler: Function,
  captureOrOptions?: boolean | AddEventListenerOption): EventHandler;

as the third parameter value is true by default, which is not usually expected.

[zewa666]

Love this idea. Just left a small remark

[zewa666]

Whats this passive prop for? I see it nowhere handled in code

[bigopon]

It is used when we pass the whole object to EventTarget.prototype.addEventListener third paramter. Same with passive in spec.

[Vheissu]

Would love to see this one merged, this is fantastic.

[stsje]

How often do you actually need this? Usually you would subscribe to events in the view <button click.delegate="">

I would keep the API as it is, and not introduce a change with minimal gains

[CLAassistant]

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