1346627 - "TypeError: this is undefined [Learn More]" can be improved

Status: RESOLVED DUPLICATE of bug 1259822

(Core :: JavaScript Engine, defect, P3)

Description

[Peter Bengtsson [:peterbe]]

Attachment: Screen Shot 2017-03-12 at 7.30.50 AM.png

Attached is a screenshot showing the same error message in Firefox 54 and (in the background) Chrome 56.

The Chrome error is vastly more helpful.

Comment 1

[J. Ryan Stinnett [:jryans] (Use needinfo, replies may be slow)]

I suspect the JS team would need to improve this type of message.

Comment 2

[Jim Michaels]

TypeError: undefined has no properties[Learn More]
just what variable is undefined in all of what's on that line? once context is out of that function, vars are out of scope, so I can't just use the console to look at them individually or even at expressions. and there is a lot of lines to trudge through for debugging, so give me a clue what variable is the problem please.

Comment 3

[Jim Michaels]

"1234"[5]
TypeError: undefined has no properties[Learn More]
a proper error message is that "index (5) is out of bounds"

var i=5;
"1234"[i]
TypeError: undefined has no properties[Learn More]
a proper error message is that "index i (5) is out of bounds"

it's not a property getter or setter, so what's normally given is the wrong error message.

Comment 4

[Tooru Fujisawa [:arai]]

we're throwing from ToObjectSlow, with ReportIsNullOrUndefined.
maybe we could pass more context to ToObject* functions.

Comment 5

[Tooru Fujisawa [:arai]]

I cannot reproduce the error on the codepen tho,
this should be fixed by bug 1259822 and bug 1488417.