knockout-projections is a new Knockout.js plugin that adds efficient “map” and “filter” features to observable arrays. This means you can:
* Write myObservableArray.map(someMappingFunction) to get a new, read-only array-valued observable containing the mapped version of each input item.
* Write myObservableArray.filter(someFilterFunction) to get a new, read-only array-valued observable containing a subset of the input items.
When the underlying myObservableArray changes, or whenever any observable accessed during the mapping/filtering changes, the output array will be recomputed efficiently, meaning that the map/filter callbacks will only be invoked for the affected items.
The point of all this: it can scale up to maintain live transforms of large arrays, with only a fixed cost (not O(N)) to propagate typical changes through the graph of dependencies.
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