CODEWITHSUNDEEP
javascriptecmascript-5
Raynos
Raynos

Reputation: 169451

Why is Number.prototype a Number

({}).toString.call(Number.prototype) === "[object Number]"

The Number prototype object is itself a Number object (its [[Class]] is "Number") whose value is +0.

15.7.4

Why would it be useful for Number.prototype to be a Number? (the same goes for every other built-in prototype which has the [[Class]] set to not Object)

I'm picking on Number.prototype specifically because I can imagine sensible legacy reasons for Array.prototype and Date.prototype.

Upvotes: 16

Views: 411

Answers (2)

Domenic
Domenic

Reputation: 112857

In general, Constructor.prototype is an exemplar of the "type" defined by Constructor. Although things seem to get hairy for immutable primitives, and especially once you involve the boxing stuff, this exemplar concept still makes sense, with 0 being the "exemplar" of Number.

Upvotes: 1

RobG
RobG

Reputation: 147453

The Number prototype object is itself a Number object (its [[Class]] is "Number") whose value is +0

Why wouldn't Number.prototype be a Number object? Its [[Prototype]] is Object.prototype, so it still inherits from Object.

Upvotes: 1

Related Questions