immutable JS

tc39/proposal-record-tuple: ECMAScript proposal for the Record and Tuple value types. | Stage 1: it will change!

his proposal introduces two new deeply immutable data structures to JavaScript:

• Record, a deeply immutable Object-like structure #{ x: 1, y: 2 }
• Tuple, a deeply immutable Array-like structure #[1, 2, 3, 4]

Today, userland libraries implement similar concepts, such as Immutable.js.