[notSorella]

And where would JavaScript not handle them in a way people don't expect them to be handled?

Comparing Python's handling of semicolons with JavaScript's ASI, you get the following:

-- End of statements

Python and JavaScript: Ends with either a new line or a semicolon.

-- Line joining

Python: whitespace strict, so lines must be either explicitly joined through the `\' escape character, or put inside a parenthesized expression, which ignores whitespace.

JavaScript: non-whitespace strict, so lines don't need to be explicitly joined. Statements may be continued by starting the following line with a continuation token (one of: `[ ( + - /')

-- Exceptions

Python: Parenthesized expressions use a different parser state (ie.: whitespace strict vs non-whitespace strict)

JavaScript: restricted production grammar usually have optional expressions following them, and since they are a valid statement on their own, the statement will be ended with a new line. So, the related information must start in the same line.

Restricted productions are: return, break and continue; Post-fix and prefix operators are included as restricted productions for readability's sake.

I fail to see how that's difficult to remember, or how that's insanely more complex than Python's rules...

[agscala]

It's mostly because of the way JavaScript handles your 'line joining' point. It's not great, and it's easy to shoot yourself in the foot.

[notSorella]

I really don't see any problem with the way JavaScript handles it. "Unless the following line can be part of the preceding statement, end the current statement" is a pretty natural thing to me. But well, I guess that's a matter of taste, and you can't really discuss that...

[sid0]

Yes, the line joining is precisely where people trip up, the classic example being

  return
  { foo: bar }

[notSorella]

That's not a problem with the line joining stuff. Both `return' and `{ foo: bar }' are ENTIRE VALID statements in their own right.

returnStmt ::= "return" [ expression ] (";" or EOL)

Note that expression is optional, so it's the choice of `return' by itself being a valid statement on its own that "causes problems".

Plus, this is not really a problem that can be solved by simply putting semicolons everywhere. You can't change the parser rules by including or not semicolons.

Also, same thing with break/continue:

breakStmt ::= "break" [ label ] (";" or EOL)

continueStmt ::= "continue" [ label ] (";" or EOL)

[cdsanchez]

`return` may be a valid statement but an object literal is not.

A standalone object literal would likely be interpreted as a block and would throw a syntax error unless it were a simple identifier and a statement `{ foo: <statement> }`, in which case it would not interpret it as an object but exactly what it is, a label and a statement.

This is why JSON parsers which use eval must first wrap the object literal with parens, to make it an expression rather than a statement.

[notSorella]

Never said it was an object literal eh. Object literals can only occur inside expressions, that's pretty well defined in the JavaScript AST too, which is described to the utmost detail in the ECMAScript specs.

The thing is:

- `return` alone is a valid statement in its own.

- The parser just need to use a simple lookahead to decide whether the next line is part of the previous statement.

- The parser DON'T change the meaning of your programs.

All that's beside that is a matter of taste. Whether use semicolons or not is up to what sits better with each person. I'm just arguing against the silly and incorrect "technical" arguments against it.