Question

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Are “(function ( ) { } ) ( )” and “(function ( ) { } ( ) )” functionally equal in JavaScript?

My question having these special characters, I couldn’t find a good answer. (Does anyone know how to search with them?)

I’ve seen two patterns to immediately calling anonymous functions http://jsfiddle.net/ukqS8/1/

(function(d) {
    document.write(d*2);
})(3);

and

(function(x) {
    document.write(x*2);
}(3));

The difference being where (3) is placed: inside or outside the closing parenthesis.

I found a good explanation for the second case here:

javascript function vs. ( function() { … } ());

which I understood as function(x) {...} creates a function object, (3) becomes its argument, and the enclosing () tells the interpreter that what’s inside is a statement.

In the first case, it appears to make (function(d) {...}) a statement that somehow is also a function, and then apply (3) to this statement/function.

So, they both appear to execute the same way. Is there really a difference here? Scope (I doubt it)? Is either option preferable?

Answer 1

Your understanding is incorrect.

Those are both function expressions; the placement of the parentheses makes no difference here.

However, there can be a subtle difference.