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.
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 WiseIn this version of the...