Can we assign Array to the key of Record and Object in index of Tuples in Javascript?

Question

ES15 has introduced Records and Tuples, So can we use array as a attribute value inside the Record? Can we use object as a value of Tuple index?

1. Is it a valid for Record ?

const user = #{
  name: "Avyukt",
  age: 39,
  hobbies: ['sleeping', 'eating', 'crying'] // Is it a valid add arr 
}

2. Is it a valid Tuple?

const user = #[ 
    { name: "Avyukt", age: 1 }, // Is it valid to add object as a value
    { name: 'Reyansh', age: 5 } 
]

Answer 1

This part of the proposed specification:

https://github.com/tc39/proposal-record-tuple/blob/5c9a6e144c687ef5911f4c0c088bc21343cbaf68/README.md?plain=1#L252

Records and Tuples may only contain primitives and other Records and Tuples. Attempting to create a Record or Tuple that contains an Object (null is not an object) or a Function throws a TypeError.

No, a tuple may not contain an object, but it can contain a Record, in the current proposal

Likewise, a record may not contain an array value, but it can contain a tuple.

I would caution against the title that ES15 has introduced anything.

This is currently a stage 2 proposal only.

Answer 2

As Adam pointed out in their answer, in the current iteration of the proposed spec you can't store objects (including arrays) in records or tuples, otherwise you'll get a TypeError. The escape hatch the spec authors suggest is the use of a Symbol with a Map. The idea is to place a Symbol in the place of your object/array within your record/tuple. The Symbol is then used as a key in a Map, allowing you to essentially dereference the symbol by looking up its corresponding value in the Map, for example:

const RefsRegistry = new WeakMap(); 
const hobbiesRef = Symbol("hobbies");

RefsRegistry.set(hobbiesRef, ['sleeping', 'eating', 'crying']); // ECMAScript 2023 (ES14) now allows for Symbols in WeakMaps

const user = #{
  name: "Avyukt",
  age: 39,
  hobbies: hobbiesRef
};

Now the above record is valid, since it no longer contains an array, but rather holds a Symbol, and as that's a primitive it's allowed.

When reading the value, you would need to dereference the Symbol using the Map, for example:

const hobbies = RefsRegistry.get(user.hobbies);