Immutable.Map

Map is the immutable version of JavaScript's object structure. Due to JavaScript objects having the concise object literal syntax, it's often used as a key-value store with key being type string. This pattern closely follows the map data structure. Let's revisit the previous example, but use Immutable.Map instead.

import * as Immutable from 'immutable';

let movie1 = Immutable.Map<string, any>({
  name: 'Star Wars',
  episode: 7
});

let movie2 = movie1;

movie2 = movie2.set('episode', 8);

console.log(movie1.get('episode')); // writes 7
console.log(movie2.get('episode')); // writes 8

Instead of binding the object literal directly to movie1, we pass it as an argument to Immutable.Map. This changes how we interact with movie1's properties.

To get the value of a property, we call the get method, passing the property name we want, like how we'd use an object's string indexer.

To set the value of a property, we call the set method, passing the property name and the new value. Note that it won't mutate the existing Map object - it returns a new object with the updated property, so we must rebind the movie2 variable to the new object.