anonymous javascript function call !function vs function

Question

How come

function(){ alert("test123");}()

produces SyntaxError: Unexpected token (

while

!function(){ alert("test123");}()

alerts "test123"

?

http://benalman.com/news/2010/11/immediately-invoked-function-expression/ — zerkms, Aug 27 '13 at 08:13
@zerkms You should probably post that as an answer, as it actually explains the heart of the matter quite well. — Kippie, Aug 27 '13 at 08:15
For even more fun. Anything that must be evaluated in an expression also does this: `-function(){}()`, `+function(){}()`,`0|function(){}()` etc — slebetman, Aug 27 '13 at 08:22

Anatolii Gabuza · Accepted Answer · 2013-08-27T08:28:27.027

3

It's because by adding ! sign you convert the declaration into an expression and invoke it immediately. By enclosing your function into brackets you will make first example working without errors:

(function(){ alert("test123");})()

To make it clearer you can think about first expression as something like:

if (false || !function(){ return false; }())

And as @zerkms noticed there is a complete explanation of Immediately-invoking functions.

edited Aug 27 '13 at 08:28

answered Aug 27 '13 at 08:15

Anatolii Gabuza

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too bad I can't write a proper answer, but... "identifier" is not the correct term. Rather the distinction is between a definition and an expression. The former cannot be immediately invoked. – John Dvorak Aug 27 '13 at 08:18
1

Right track but wrong explanation. The ! converts the declaration into an expression. – slebetman Aug 27 '13 at 08:18
I can define a function and _not_ invoke it: `!function(){alert("will not be called")}` – John Dvorak Aug 27 '13 at 08:20
@slebetman Thanks. Updated. – Anatolii Gabuza Aug 27 '13 at 08:22

anonymous javascript function call !function vs function

1 Answers1