Lazy mapping

The mapping that we've done so far has been called directly on collections. Mapping operations can be done lazily as part of a sequence of transformations that feed into a side-effect. Being able to filter and map lazily is part of a pattern that you'll use frequently with Immutable.js.

Multiple map() calls

Let's revisit our earlier example where we transformed two map values into a single capitalized name string:

const capitalize = s =>
  `${s.charAt(0).toUpperCase()}${s.slice(1)}`;
const myList = List.of(
  Map.of('first', 'joe', 'last', 'brown', 'age', 45),
  Map.of('first', 'john', 'last', 'smith', 'age', 32),
  Map.of('first', 'mary', 'last', 'wise', 'age', 56)
);

myList
  .toSeq()
  .map(v => v.update('first', capitalize))
  .map(v => v.update('last', capitalize))
  .map(v => [v.get('first'), v.get('last')].join(' '))
  .forEach(v => console.log('name', v));
  // -> name Joe Brown
  // -> name John Smith
  // -> name Mary Wise

In this version of the...