SyntaxError for function(){}()

Question

Please see this fiddle. For me, it's just a self-executing empty function:

function(){}()

Google Chrome 16.0.912.4 dev-m returns the error:

Uncaught SyntaxError: Unexpected token (

Why? This is especially strange because adding extraneous brackets will remove the error:

(function(){})()

it seems like the browser expects a name after `function` using this notation — Fender, Oct 22 '11 at 16:23
Related: http://stackoverflow.com/questions/423228/difference-between-function-and-function — Digital Plane, Oct 22 '11 at 16:25
Firefox gives the same error. That's because `function(){}` is the actual function you want to execute. So you have to add brackets around it to indicate that you mean the whole function! — ComFreek, Oct 22 '11 at 16:25
Also interesting is that `x=function () {} ()` does not throw an error. — kojiro, Oct 22 '11 at 16:29
@kojiro Maybe the browser interprets it as `(x=function () {}) ()`. — ComFreek, Oct 22 '11 at 16:30
@kojiro: If you have an assignment, everything on right side is an expression. — Felix Kling, Oct 22 '11 at 16:31
@ComFreek: No it does not, it is the same as `x = (function(){})();` — Felix Kling, Oct 22 '11 at 16:32
@ComFreek Actually the assignment is enough of a clue to let the interpreter know that it's a function expression and not a function *declaration*. This is covered in the question linked above, and also more thoroughly in [What is the difference between a function expression vs declaration in Javascript?](http://stackoverflow.com/questions/1013385) — kojiro, Oct 22 '11 at 16:34
@FelixKling You're right! Interesting link ;) By the way even IE 6 can handle such declarations! — ComFreek, Oct 22 '11 at 16:34

score 8 · Accepted Answer · answered Oct 22 '11 at 16:23

8

ExpressionStatement :

[lookahead ∉ {{, function}] Expression ;

Because a function () {}() is not a statement as defined in ES5.1

And a valid program has to be a statement.

however the following

!function () {}();

is a valid statement, so is using () and so is var ret = function () {}()

answered Oct 22 '11 at 16:23

Raynos

Why is `function(){}()` not a statement. It is the statement "execute the empty function", isn't it? – Randomblue Oct 22 '11 at 16:29
2

@Randomblue: There are two ways to interpret this and the standard is to interpret it as function declaration, which requires a name. – Felix Kling Oct 22 '11 at 16:30

1 Answers1