Mastering Immutable.js

Avoiding unnecessary work

The goal of using lazy evaluation is to avoid unnecessary work. When you're dealing with large collections, there are a lot of values that you don't need. Think about a user interface that displays a list. The source of the list is a collection of values. Since you're only displaying a small portion of this list in the UI, it doesn't make sense to process the whole thing.

Lazy evaluation avoids processing the entire collection by only processing one value at a time and on demand. The idea is that a side-effect is responsible for rendering this list in the UI. The side-effect knows that there is a need to display only 20 items in this list. As this side-effect iterates over a sequence of transformations, it asks the ...