introspection of bind functions

💡 Ideas
1

Similar to instanceof, a way to introspect if two bound functions share the same function, for example:

let a = () => {}
let b = a.bind()
let c = b.bind()
console.assert(b.instanceof(a))
console.assert(c.instanceof(a))

Whether "c.instanceof(a)" (the second assert) should return true is out there.

2

Hi @thysultan !

Interesting idea. Do you have some particular situations where this would help? TC39 proposals are often considered based on how well they address a problem (amongst other factors too of course).

3

Here are a few:

  • When using bound functions as a reactive boxed values, in places that the bound function is used, in order to determine the "color" of the function whether it is a reactive function created internally or an external function and take differing branches based on that.
  • determining if an event listener shares the same function "instance".
  • short circuit on equality comparison when functions share the same internal "instance" to avoid memoization invalidation etc...
4

For the first, storing the bound functions in a weak collection, or adding a Symbol property on them, seems like it'd suffice?

Additionally, you could memoize the input function so that there's only ever one bound copy of it - which would make it easier to map back from the bound function to the original one.

5

All definitely possible as it stands, the second more so if the consumer and provider are the same, otherwise there's a lot of state hustling to get it to that state.