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claudepache / es-legacy-function-reflection

JavaScript: Legacy reflection features on functions needed for web compatibility
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Use a less generic name for the IsLeakableFunction abstract operation #7

Closed claudepache closed 4 years ago

claudepache commented 4 years ago

The IsLeakableFunction operation introduced in this proposal is intended to be used specifically in the scope of this proposal, and we shouldn’t encourage its use as a generic tool for discriminating between good and bad functions.

Indeed, it should normally not be detectable whether a function is implemented in strict ES, sloppy ES, or Fortran.

Precedent: “undefined-like object” was changed to “has an [[IsHTMLDDA]] internal slot”.

hax commented 4 years ago

It's already possible to detect strictness of a function object f by simply check whether f.caller throw. (Though theoretically it can only detect non-strict function declaration/expression)

claudepache commented 4 years ago

When I say that the implementation technique of a function should not be detectable, it is specifically so that both implementations and users may refactor the code they control without provoking too much breakage when entering in contact with unrelated or poorly written third-party code.

Of course, this is not a reasonable hard constraint for Function#caller and Function#arguments, and even for Function#toString(). But we should strive to limit the set of functionalities for which the problem will occur.

claudepache commented 4 years ago

The IsLeakableFunction operation introduced in this proposal is intended to be used specifically in the scope of this proposal, and we shouldn’t encourage its use as a generic tool for discriminating between good and bad functions.

In fact, ECMA-262 has already a name for “bad” function objects: it is the so-called non-strict functions. The specific abstract operation defined in the scope of this proposal uses more severe criteria, because it has additional goals: deprecate the functionality, follow de-facto semantics, etc.