Stage 0
Classification: API Change
Human Validated: KW
Title: Reflect.{isCallable,isConstructor}
Authors: Caitlin Potter
Champions: Caitlin Potter
Last Presented: None
Stage Upgrades:
Stage 1: NA
Stage 2: NA
Stage 2.7: NA
Stage 3: NA
Stage 4: NA
Last Commit: 2020-11-06
Topics: others functions
Keywords: legacy framework
GitHub Link: https://github.com/caitp/TC39-Proposals/blob/HEAD/tc39-reflect-isconstructor-iscallable.md
GitHub Note Link: None
Proposal Description:
Function.isCallable() / Function.isConstructor()
Why are these useful?
- Help support classes/other new function definitions in legacy framework code without significant changes
- Expose a pretty important part of the runtime to applications, who also may wish to use them
- Not require depending on slow (and inconsistent across implementations)
Function.toString()processing or try/catch statements
The very tiny normative language:
Function.isCallable ( argument )
When the isCallable function is called with argument argument, the following steps are taken:
- If IsCallable(argument) is false, return false.
- If argument has a IsClassConstructor internal slot with value true, return false.
- Return true.
(Should be “Return IsCallable(argument)”, but adjusted to not report Class constructors as callable, as they throw unconditionally without invoking any author code)
Function.isConstructor ( argument )
When the isConstructor function is called with argument argument, the following steps are taken:
- Return IsConstructor(argument).