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It is evident that xstream, with the two methods addListener and removeListener, is able to reroute streams (change their sources and sinks) dynamically. I see no equivalent with mostjs. Does most only let you lay out the routing of the streams once? If so, is this static nature what allows mostjs to optimize for such superior performance?

Also, xstream uses an imitate method that lets it feature circular dependencies. Is there any way to achieve circular dependency with mostjs?

Joseph Johnston
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There are many functions in most.js that operate on both a Source and a Sink, e.g., map(), which transforms all the events in a stream, acts as a Sink by consuming events, and as a Source when producing new event values after applying a function to them. observe() is an example of a particular kind of Sink that consumes events, and passes them to a function you provide.

Most.js Streams are not active until you consume them, by using one of the "terminal" combinators, observe, drain, or reduce. When you call one of those, the Stream sends a signal in the Source-Sink chain to the Source at the very beginning of the chain. That producer Source will then begin producing events.

Events are then propagated synchronously from the Source through the Source-Sink chain by a simple method call.

Thus, you could provide your own "listener" function to a map which would transform the events.

There are many factors contributing to most.js’s performance.

The simple call stack event propagation architecture, plus hoisting try/catch out of combinator implementations were two of the earliest and biggest performance improvements.

Most.js performs several other optimizations automatically, based on algebraic equivalences. A relatively well-known example is combining multiple map operations, e.g. map(g, map(f, stream)), into a single map by doing function composition on f and g.

The operation also combines multiple filter operations, multiple merge operations, multiple take and skip, among others. These optimizations reduce the number of method calls needed to propagate an event from producer to consumer.

See this interview with Brian Cavalier

Most.js itself doesn’t handle circular dependencies, but it is totally possible using most-proxy. Motorcycle does this to create its cycle in its run package.

Frederik Krautwald
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have you seen this issue regarding xstream.js imitate in most.js?https://github.com/cujojs/most/issues/308

tgk
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