! preceding function in javascript? [duplicate]

The preceding ! takes the un-parseable statement, and allows it to to be parsed by the JS engine, which in turn returns true.

function(){}();
SyntaxError: Unexpected token (

!function(){}();
>>true

It simply makes the JavaScript parser parse it as an expression, which is necessary to execute it.

I've tried it, it returned true. The function returns undefined, and !undefined is true.

!function(){}();
^          ^ ^
C          A  B

• A. function(){} is an empty anonymous function
• B. () executes the function (A), returning undefined
• C. ! negates undefined, which becomes true

I think they used that trick for a code golf or an obfuscated code. It is a bad practice to practially use that

Try javascript:alert(!function(){}()) in your browser address bar