--- title: Immutable.js category: JavaScript libraries layout: default-ad --- ```js var Immutable = require('immutable') ``` ## Maps ```js var map = Immutable.Map({ a: 1, b: 2, c: 3 }) map .set('b', 50) .get('b') // 50 ``` ## Lists ```js var list = Immutable.List.of(1, 2) list .push(3, 4, 5) .unshift(0) .concat(list2, list3) .get(0) .size ``` ## Nested maps ```js var nested = Immutable.fromJS({ user: { profile: { name: 'John' } } }) nested .mergeDeep({ user: { profile: { age: 90 } } }) .setIn([ 'user', 'profile', 'name' ], 'Jack') .updateIn([ 'user', 'profile', 'name' ], (s) => s.toUpperCase()) .getIn(['user', 'profile', 'name']) // 'JACK' ```