In short: You modified functions list.

Here is the test case in js:

Test.assertEquals(JSON.stringify(chained(fns)(r)), 
                  JSON.stringify(_solChained(fns)(r)),
                  "Random test "+i)

I suggest modify test case to:

Test.assertEquals(JSON.stringify(_solChained(fns)(r)),
                  JSON.stringify(chained(fns)(r)), 
                  "Random test "+i)

With that, we can pop as we wish......

Indeed. I try to fix it....Thank~

Yes, if there is any other identifier named "func", it hides the function from the outer environment.

Are you mean something like this?

defaultArguments(add, {func: 1});

Fails (with TypeError) on this one:

function foo(func) { return func; }

The hardest part of this kind of solutions is generating unique identifiers.