Feature request: Add more option for keyCode value in the event input-throttled

Hi, currently I’m working on search suggestion component. Im finding a solution for when the suggestion box is expanded the user enable use keyboard arrows( up, down) for selecting. I think we can not done it without having event.keyCode value in keydown event for element input. I check the file https://github.com/ampproject/amphtml/blob/master/src/service/action-impl.js
My idea is change the event listener from input to keydown.

const throttledInput = throttle(this.ampdoc.win, event => {
        const target = dev().assertElement(event.target);
        this.trigger(target, name, /** @type {!ActionEventDef} */ (event),
            ActionTrust.HIGH);
}, DEFAULT_THROTTLE_INTERVAL); 
this.root_.addEventListener('keydown', event => {
        const deferredEvent = new DeferredEvent(event);
        this.addTargetPropertiesAsDetail_(deferredEvent);
        throttledInput(deferredEvent);
      });

and in function addTargetPropertiesAsDetail_ add the keyCode value

  if (event.keyCode !== undefined) {
        detail['keyCode'] = event.keyCode;
    }

I still not built the development environment yet so I havent tested yet. But it’s good if we can add more value like this.

[cathyxz]

Yes, and that does work in the AMPStart example. Maybe my copied code block isn’t sufficiently precise. I’ll churn up a codepen.

Edit: to be precise, the the ampstart travel example, the autosuggest for “Where do you want to go?” allows keyboard navigation of the results list via up and down keys, meaning that there is a workaround for this particular use case. Input-throttle doesn’t allow you to bind arbitrary keys, which could still be an interesting FR. Codepen incoming.

[cathyxz]

Here’s a minimal codepen. Unfortunately yes it does rely on datalist for the keyboard navigation. Oh well. Deferring to @cvializ.