Possible Duplicate:
Location of parenthesis for auto-executing anonymous JavaScript functions?
Sometimes I see:
(function() { ... }());
and sometimes I see:
(function() { ... })();
I see both forms with and without arguments. They both execute the anonymous function.
Is there a difference between the two forms? Are there any compelling reasons to use one form over the other?
There is no practical difference in those two forms, but from a grammatical point of view the difference between the two is that The Grouping Operator - the parentheses - will hold in the first example a CallExpression, that includes the FunctionExpression:
CallExpression
| |
FunctionExpression |
| |
V V
(function() { }());
^ ^
|--PrimaryExpression --|
In the second example, we have first a whole CallExpression, that holds the FunctionExpression:
PrimaryExpression
|
FunctionExpression
|
V
(function() { })();
^ ^
|-- CallExpression --|
There is no difference between the two, so far as the compiler is concerned. However, will find that the (function () {}()) style is recommended in Douglas Crockford’s JavaScript code conventions.
As far as differences go, it is really just syntactic sugar. Somewhat equivalent to: "do you like jQuery() or $()?" Both can be compiled, executed, and used interchangeably (AFAIK).
From the code samples I have seen thus far, more people seem to follow the Crockford code convention:
(function() { ... }());
Personally, I prefer the (function(){})(); convention because it is more apparent to me that the function is self-executing; I'm also a big user of jQuery and that's the convention used in jQuery source.
Additionally, it is considered good practice to use parens to enclose your self-executing function, regardless of which form you choose to go with.
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