418573 - Say "is undefined" or "is null" instead of "is not a function" when appropriate

Status: ASSIGNED

(Core :: JavaScript Engine, enhancement, P5)

Description

[Jesse Ruderman]

js> ({}).b()
typein:14: TypeError: {}.b is not a function
js> ({}).b.c
typein:16: TypeError: {}.b is undefined

I think we should use the more specific error message "is undefined" for attempted function calls too.  (The old message "has no properties", which was replaced by "is null" / "is undefined" in bug 353116, wouldn't have made sense in this context.)

Comment 1

[Daira Hopwood]

Shouldn't it be "is not callable" (when not undefined or null)? Non-functions can be callable.

Comment 2

[Tooru Fujisawa [:arai]]

I'm wondering about the wording...

Safari
  > ({}).b()
  < TypeError: ({}).b is not a function. (In '({}).b()', '({}).b' is undefined)

Google Chrome
  > ({}).b()
  VM55:1 Uncaught TypeError: {}.b is not a function
    at <anonymous>:1:6

Edge
  > ({}).b()
  Object doesn't support property or method 'b'

Comment 3

[Tooru Fujisawa [:arai]]

WIP patch:
  js> ({}).b()
  typein:1:6 TypeError: (intermediate value).b is undefined, not callable

the behavior seems to be changed at some point and we don't say ({}) for this case (even without patch)

other case:
  js> ({b: null}).b()
  typein:1:13 TypeError: ({b:null}).b is null, not callable

if the decompiled string is null/undefined, the previous message is used:
  js> null()
  typein:4:1 TypeError: null is not a function
  js> undefined()
  typein:5:1 TypeError: undefined is not a function

Comment 4

[Tooru Fujisawa [:arai]]

Attachment: (WIP) Report the value type when throwing not-function/not-constructor error.

WIP patch here.

there are more places that uses JSMSG_NOT_FUNCTION/JSMSG_NOT_CONSTRUCTOR.
I'll check them later.

Comment 5

[Tom S [:evilpie]]

Chrome also uses "is not a function". I suspect most JS developers don't really know the difference between callable and a function.

> ({}).b()
TypeError: {}.b is not a function