thenSource of if() still running even though condition is false

[WhatsThatItsPat]

RxJS version:
5.4.2

Code to reproduce:

I have an issue where Observable.if() isn't protecting me against a null value like I expect it would.

If I have a variable, whatever, that can be null or a simple object...

let whatever = null;
// or
whatever = {something: 'abc123'};

...and if I use Observable.if() like this...

Rx.Observable.if(
  () => !!whatever,
  Rx.Observable.of(`true: ${whatever.something}`),
  Rx.Observable.of('unprotected condition false')
).subscribe(next => {
  console.log(`unprotected:`, next);
});

...when whatever is null, I get an error: Cannot read property 'something' of null.

Shouldn't the false condition stop the thenSource from running?

If I "wrap" the thenSource stream in a switchMap, it works; I'm protected from the null value and the elseSource runs.

Rx.Observable.if(
  () => !!whatever,
  Rx.Observable.of('discard')
    .switchMap(discard => Rx.Observable.of(`true: ${whatever.something}`)),
  Rx.Observable.of('condition false')
).subscribe(next => {
  console.log(`protected:`, next);
});

Additional information:

Here's a codepen to play with:
https://codepen.io/patrickmcd/pen/BZeeQK?editors=0010

[paulpdaniels]

The of isn't running but you are setting up the initial value immediately by doing

`true: ${whatever.something}`

That isn't an RxJS issue it is a javascript one. Personally I have always wished that if was passed function that created Observables rather than just being fed raw Observables. But if you want to work around it you can do as you did or you can do:

Observable.if(
  () => !!whatever,
  Observable.defer(() => Observable.of(`true: ${whatever.something}`))
)

[WhatsThatItsPat]

Got it. At least I'm not going crazy.

Put another way, I think, is that the word "if" has fooled me into expecting it to work as an if/else statement, and caused me to forget that if() is just a function.

Thanks for the defer tip. That looks way less hacky than my solution.

And congrats on the book release btw. I'm looking forward to another read when I get my dead tree version.

[paulpdaniels]

No problem and thanks!

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