Microtask scheduler for reducers

Reducers used to be applied synchronously, now they are applied at the end of the current event loop using the microtask scheduler. See issue #61 for more context.

Also fixed pickMerge to ignore undefined sink streams, and fixed pickCombine to refuse (by throwing an error) undefined sink streams. See issues #58 and #64.

Collections

Version 4 introduces "Collections", a way of efficiently and simply handling lists of many components.

makeCollection allows you to pass some configuration parameters, and returns a normal sources=>sinks Cycle.js component:

const List = makeCollection({
  item: Child,
  itemKey: (childState, index) => String(index),
  itemScope: key => key,
  collectSinks: instances => {
    return {
      onion: instances.pickMerge('onion'),
      DOM: instances.pickCombine('DOM')
        .map(itemVNodes => ul(itemVNodes))
    }
  }
});

• item required parameter: specify the item component for the list of items
• itemKey optional parameter: given state and (array) index, specify the unique identifier (key) for each item. Defaults to array index.
• itemScope optional parameter: given the item key, determine the isolation scope for that item. Defaults to null.
• collectSinks required parameter: a function specifying how to collect together all the sinks from all item components. Takes instances as input, where instances has two functions pickMerge and pickCombine, which work like pick+mix(merge) and pick+mix(combine), respectively.

Once List component is created, you can use it:

const listSinks = isolate(List, 'list')(sources);

This means sources.onion.state$ should be a stream that emits state objects with the shape {..., list: [...]}, in other words, there should be a list property that is an array. The use of isolate is optional, as long as List receives a stream of arrays under the onion channel. This is how the List knows how to create item components as the array dynamically grows or shrinks.

Note that in this version, pick and mix were removed. Instead, we have pickMerge and pickCombine.

Support also xstream v7.0

Both xstream v7.0 and v6.0 are supported now. This specially affects TypeScript users who may depend on the typings. The typings for xstream v6.0 are not compatible with xstream v7.0, even though they look the same.

Fix bug with circular infinite loop

onionify now does object reference checks to prevent the (exactly) same
object reference to be emitted consecutively. Internally, this uses
dropRepeats.

BREAKING CHANGE:
Just in case you were relying on buggy behavior, this library will no
longer emit redundant/duplicate references of state. Overall this
improves reliability, but also performance, to some extent. For most
users, this should be super safe to upgrade.