filterBy activation

[iofjuupasli]

var Kefir = require("kefir");
var a = Kefir.sequentially(1000, [1, 2, 3]);
var b = Kefir.sequentially(1000, [false, false, false]);
a.filterBy(b).log();
console.log(a._active); // true

Seems that a shouldn't be active until b is truthy

[rpominov]

Yeah, you're probably right. And same for skipUntilBy.

Also marking this as [breaking] because this change may potentially break people's code.

[iofjuupasli]

Does it means, that in case a.filterBy(b) errors from a will not flow?

[rpominov]

Hm, yes. I'm not sure which behavior is better here then.

[iofjuupasli]

should be ended if primary was ended also can't be implemented. Only when secondary is truthy.

My case for deactivation - I have external process which is represented as endless stream. It starts external process in stream declaration, and ends it using callback in stream declaration for deactivation. It's important to have child process only when application needs it, listen to it. There is another observable which declare whether this stream required now.

So for my case:

a$.flatMapLatest(a => a ? external$ : Kefir.never())

And it works ok for me. Its behavior almost same as external$.filterBy(a$) except things discussed here.

So we can leave filterBy as is for cases when 'errors' and 'end' are important, and it's ok that primary activated.

[rpominov]

Sounds good to me. I'll close this then, and we can revisit this later.