In this example, a GitHub username searchbox is rendered to the screen. The searchbox includes a typeahead, which fetches username suggestions based on what the user has typed so far.

When a user clicks on a suggestion, or presses the return key while the textbox (or a suggestion) is focused, the selected GitHub account's data is fetched, and rendered to the screen.


Two sources are observed in this example:

  • The search prop.

  • The selection prop.

The search prop is used as the source for two separate streams.

First, a stream of suggestions. Each time the search prop changes, if its value is truthy, it is debounced and sent through a pipeline which includes an asynchronous fetch request, and some data manipulation.

In a separate stream of logic, each time the search prop changes, if its value is an empty string, it is mapped to another setState effect which resets the suggestions state to an empty array.

Finally, a stream of users. Each time the selection prop changes, it is sent through a similar logic pipeline to the first stream, which results in the user state being updated.

These three streams are merged into one, and returned as the output of the aperture.

Note that all three streams used a toState "effectCreator" function at the end - this is a helper function similar to a redux actionCreator.


If the effect's type is SET_STATE, the handler passes the effect's payload into initialProps.setState.


The end result is an intelligent user interface which exposes search suggestions and fetches user data as a side-effect.

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