JS Built-in: Map and Set collections #101

Implement the Map and Set collection built-ins.

Scope#

Map#

• Map() constructor (optionally from iterable of [key, value] pairs)
• Map.prototype.set(key, value) — returns the Map (for chaining)
• Map.prototype.get(key) — returns value or undefined
• Map.prototype.has(key) — returns boolean
• Map.prototype.delete(key) — returns boolean
• Map.prototype.clear()
• Map.prototype.size (getter)
• Map.prototype.forEach(callback, thisArg?)
• Map.prototype.keys(), values(), entries() — return iterators
• Map.prototype[Symbol.iterator]() — same as entries()
• Key equality: SameValueZero (like === but NaN === NaN)
• Keys can be any value type (objects, primitives)
• Insertion order preserved

WeakMap (basic)#

• WeakMap() constructor
• get, set, has, delete
• Keys must be objects (not primitives)
• Entries are weakly held (GC can collect if no other references)

Set#

• Set() constructor (optionally from iterable)
• Set.prototype.add(value) — returns the Set
• Set.prototype.has(value) — returns boolean
• Set.prototype.delete(value) — returns boolean
• Set.prototype.clear()
• Set.prototype.size (getter)
• Set.prototype.forEach(callback, thisArg?)
• Set.prototype.keys(), values(), entries() — return iterators
• Set.prototype[Symbol.iterator]() — same as values()
• Value equality: SameValueZero
• Insertion order preserved

WeakSet (basic)#

• WeakSet() constructor
• add, has, delete
• Values must be objects

Acceptance Criteria#

• Map stores and retrieves key-value pairs correctly
• Map preserves insertion order
• Map handles object keys and NaN key equality
• Set stores unique values correctly
• Set preserves insertion order
• WeakMap/WeakSet accept only object keys/values
• Iterators (keys, values, entries) work correctly
• forEach works with proper this binding
• Unit tests for all methods and edge cases

Phase 10 — JavaScript Engine (issue 12 of 15). Depends on: JS core built-ins.