Acorn rejects call expression on the lhs of assignment. about acorn

[kspalaiologos]

@RReverser's now-deleted remark on early errors is valid, I think: I was not aware of these. Maybe it would be nice to have a mode to disable them, though. Also, despite e.g. this being an early error, acorn doesn't seem to catch it... Am I missing something? Node:

> let a = 5;
undefined
> const a = 5;
Thrown:
SyntaxError: Identifier 'a' has already been declared

More curiosities:

> let (let);
Thrown:
ReferenceError: let is not defined

vs Acorn's The keyword 'let' is reserved (1:0).

I am currently trying to parse a dataset of JavaScript code, but its language semantics are making me very close to giving up :P.

[RReverser]

It's an early error, which is different from syntax error but treated the same way.

[bakkot]

The fact that if (false) f() = x parses in browsers but not in the specification is a known deficiency of the specification which we haven't gotten around to fixing.

On the subject of early errors, I would not recommend treating early errors differently from other parse failures. The spec treats whether something is an early error or simply not matched by the grammar as a strictly editorial question. Users should not care about that distinction.

[appgurueu]

f(x) = y

is syntactically valid JS: An assignment expression is defined in terms of left hand side expressions which can be call expressions, so I'd say acorn is wrong here.

[kspalaiologos]

Shouldn't it still pass through? After all, isn't acorn merely a parser, not a static code analysis tool.

[Kimapr]

if(0)f()=0

executes without throwing any error in Node REPL

[kspalaiologos]

@appgurueu This is weird, because LHSExpression includes NewExpression, however...

> if(0)new f()=0
ReferenceError: Invalid left-hand side in assignment
[...]
> if(0)f()=0
undefined

[marijnh]

Thanks for confirming. I'm going to close this as working as intended then.