ESNext: Immutable Datastructures in JavaScript with Records & Tuples

A new ECMAScript Proposal that I’m looking forward to is this one which introduces the Record and Tuple value types. In short:

  • Records are immutable Objects that are compared by value.
  • Tuples are immutable Arrays that are compared by value.

The proposal is currently Stage-1.

Stage-1? Stage-4?

💁‍♂️ The TC39 Committee, which is concerned with the standardization of ECMAScript, has a 5 stage process in place, ranging from stage-0 to stage-4, by which it develops a new language feature. Stage-1 is the proposal phase. Stage-4 is when a proposals becomes part of the EXMAScript Speficiation.

As it stands right now, definition of Records/Tuples goes – quite obviously – the same way you define Objects/Arrays. The only difference is that you need to prefix the # operator to them.

// Records
const record1 = #{
    a: 1,
    b: 2,
    c: 3,

const record2 = #{...record1, b: 5}; // #{ a: 1, c: 3, b: 5 }

// Tuples
const tuple1 = #[1, 2, 3];
const tuple2 = tuple1.with(0, 2); // #[2, 2, 3]

Knowing that # is already used for Private Fields, and that the proposal still is Stage-1, I can see the operator get replaced as the proposal progresses over time. Personally I’m thinking to use the $ modifier/prefix.

ECMAScript proposal for the Record and Tuple value types →

💡 Looking for more ESNext Proposals that excite me? Check out ESNext: Proposals to look forward to, a talk I’ve given on that subject.

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1 Comment

  1. Great 🙂
    There is one thing though. I’m not sure about the naming.
    I know that calling them simply by “immutable array” and “immutable object” is boring, and it’s long, but it’s easier to remember and learn. It’s a descriptive modifier before an already known concept. On the other hand Record and Touple are two completely new terminology, and can be scary for the beginners.
    There is one more thing: Record is an already existing data type of Typescript.

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