fix(RouterSource): Initialize this._history$ with _runSA.remember

[ntilwalli]

I encountered an issue where the the defined route stream was not emitting even though I could listen to the history$ and the route should have matched. I fixed it by making a common remember call on the StreamAdapter. I haven't tracked down why this fixed my issue, but I created this PR not necessarily to get it merged but to at a minimum have a discussion about the root cause.

[TylorS]

I can see how this would work with xstream, because it will continue to be a MemoryStream, but I have to say I'm very surprised the tests continue to pass with Rx 4 and Rx 5 as 'memory' only occurs where it is explicitly called. I'd love to see some example code where the previous behavior broke something if you could find the time to do so.

[ntilwalli]

I've posted a branch of my routing example repo which demonstrates the issue here: https://github.com/ntilwalli/routingWithState/tree/rememberIssue

You'll see that I explicitly add a listener to the history$. You would expect that clicking on any of the links would cause printout from both the define-stream and the history$ but only the define-stream prints... This is effectively the same issue I had except in my original it was the other way around (history$ printed and define-stream did not...) This issue gets fixed if I call remember in the constructor of RouterSource and not in the member functions.

[TylorS]

@ntilwalli Does the issue still persist if the member functions still call remember as well as adding remember to the root history$? I think they would be necessary for all other stream libraries other than xstream.

[ntilwalli]

The issue does still persist if the member functions call remember. Here's the console output

from root: Object {pathname: "/", search: "", hash: "", state: undefined, action: "POP"…}
main.js:12484 from history$...: Object {pathname: "/", search: "", hash: "", state: undefined, action: "POP"…}
main.js:12484 from root: Object {pathname: "/", search: "", hash: "", state: undefined, action: "POP"…}
main.js:12484 from define$...: Object {path: "/", location: Object}
main.js:12487 Object {count: 0}
(index):35 Live reload enabled.
main.js:12484 from root: Object {pathname: "/page1", search: "", hash: "", state: undefined, action: "PUSH"…}
main.js:12484 from define$...: Object {path: "/page1", location: Object}
main.js:12484 from root: Object {pathname: "/page1", search: "", hash: "", state: undefined, action: "PUSH"…}
main.js:12484 from define$...: Object {path: "/page1", location: Object}

After the Live reload enabled is when the page is loaded. You'll see that on page load both the define$ and the history$ (non-root, in main...) fire. After the page is loaded, when I click on the Go to page 1, the root history$ stream fires twice along with two fires of the define$ (note the non-root history$ does not fire). I would expect the root history$ to fire once, the define$ to fire once and the non-root history$ stream to fire once.

When I remove the calls to remember in the member functions and put it directly at the root, it behaves as expected.

[ntilwalli]

I've had trouble constructing a failing test-case, but it should be pretty quick to reproduce. Here are the steps:

1. Pull the repo (ntilwalli/routerWithState) I posted and switch to the rememberIssue branch
2. npm install -g live-server watchify
3. npm install
4. npm run build
5. npm run serve
6. Go to http://localhost:8080, click around and check the console...

[TylorS]

So I'm not able to reproduce. It seems to be logging everything I'd expect.

[TylorS]

The initial values from both, and from router... with each route change, and the debug() with each state change