[JS] Confusing error message

[dawkot]

Function echo outputs the wrong string.

Example

proc foo =
  var x: seq[int]
  inc x[0]

foo()

Current Output

Uncaught TypeError: Cannot read property 'length' of null
    at foo_42003 (x.js:531)
    at x.js:536

Expected Output

Information that no element of such index exists

Additional Information

$ nim -v
Nim Compiler Version 1.0.2

[metagn]

Now gives index out of bounds, the container is empty