Javascript Syntax

[1,2,3,4,].length // 4
[1,2,3,4,,].length // 5

27.toString() // Uncaught SyntaxError: Invalid or unexpected token
27..toString() // '27'

Wat.

In the former example, [1,2,3,4,,], I simply dont understand the rationale. Why is this not a syntax error!? 🤯

In the latter, 27.toString() // Uncaught SyntaxError: Invalid or unexpected token. Okay fine, not all languages support using attribute lookups on literal values like integers. Take python, for example:

>>> 1.__str__()
  File "<stdin>", line 1
    1.__str__()
      ^
SyntaxError: invalid syntax

>>> (1).__str__()
>>> x = 1
>>> x.__str__()

# Admittedly there's not a huge amount you can call on an int, necessarily. But still!
# Contrast it with something like `"".join`, and it starts to look weird!

And that’s somewhat sad because other languages do support this kind of thing (like Rust), and i think it ends up looking a lot more natural than the alternatives you get in languages that dont support it.

But back to javascript 27..toString() // '27'…wat again!?

Javascript has all sorts of weird runtime semantics that people meme about. The implicit coersions, the insane equality map, etc. But things like these should literally just be syntax errors, and I dont understand why they’re not!