1066996 - Console logs incorrect values

Status: RESOLVED DUPLICATE of bug 754861

(DevTools :: Console, defect)

Description

[Victor Porof [:vporof][:vp]]

STR:

Evaluate the following in the web console (in a single line):

var x = [42]; console.log(x); x[0] = 43;

Expected output: Array [42]
Actual output: Array [43];

This is terrifying and very, very (very!) misleading.

Suppose you have some code that looks like this:

function test(obj) {
  console.log(obj);
  ...lots of code...
  ...lots of code...
  ...lots of code...
  ...i can't even see the function name at this point...
  ...more code...
  obj.foo = 43;
  ...even more code...
}

test({ foo: 42 });

Obviously, you'd expect your console.log call to print Object { foo: 42 }. However, even if the property is modified later (and as someone who might take a look at the code for the first time, and you don't even know that the modification is happening, especially if it's buried in the code), the output is going to be Object { foo: 43 }.

This is all sorts of wrong.

Chrome does the right thing and prints the object just like it receives it.

Comment 1

[James Long (:jlongster)]

I doubt this is related, but when large objects are printed Firefox and Chrome show an interactive view and the same thing happens. That makes total sense though. Otherwise we'd have to deep copy the object...

var arr = [];
for(var i=0; i<1000; i++) { arr.push(i); }
console.log(arr)
arr[0] = 1000;

If you wait to expand the interactive view until after you change the value, it shows the updated value. Again that makes sense; the summarized string representation should always show the current snapshot like you want.

Comment 2

[James Long (:jlongster)]

My last sentence is confusing. I meant to say the interactive view behavior makes sense, *however* the summmarized string repr should always show the current snapshot.

Comment 3

[Victor Porof [:vporof][:vp]]

(In reply to James Long (:jlongster) from comment #2)
> My last sentence is confusing. I meant to say the interactive view behavior
> makes sense, *however* the summmarized string repr should always show the
> current snapshot.

I think this approach is the best compromise.

This should be made clear in the UI though, somehow. Making it obvious that the interactive inspection shows the live value would prevent any (potential) additional confusion.

Comment 4

[Girish Sharma [:Optimizer]]

I think this bug is a dupe of bug 754861

Comment 5

[Panos Astithas (he/him) [:past] (please ni?)]

It is indeed.