Feature request: allow keepalive.request() to accept a function

[VeryBueno]

I'm submitting a ... (check one with "x")

[ ] bug report => search github for a similar issue or PR before submitting
[x] feature request
[ ] support request => Please do not submit support request here, instead see https://github.com/HackedByChinese/ng2-idle/blob/master/CONTRIBUTING.md#getting-help

Current behavior

The keepalive module accepts a string or Request in request() for configuring the ping request.

Expected behavior

I'd like to have the ability to pass a function that returns a promise.

Minimal reproduction of the problem with instructions

n/a

What is the motivation / use case for changing the behavior?

I have an app that needs to add special headers to HTTP requests. I extended Angular's Http to enable this. I'd rather use a service that I already wrote instead of manually constructing the Request to pass to keepalive.request().

Please tell us about your environment:

Idea, npm, linux

• @ng-idle version: 2.x

• Angular version: 2.x

• Browser: [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]

  All

• Language: [all | TypeScript X.X | ES6/7 | ES5] All

• Node: node --version = 6.10.3

Thank you!

[moribvndvs]

You do not have to use request. If you'd like to handle the actual pinging logic yourself, just subscribe to Keepalive.onPing and do whatever you'd like.

See Extend your app component for a trivial example of how to subscribe to the event.