Self-executing functions [duplicate]

Answer 1

There isn't any difference in this case, but only because it's prefixed with:

var obj = ...

Without that, only the first version is correct, because you need the additional parentheses to allow the interpreter to correctly parse the function as a function expression and not as a function declaration.

You would of course only omit var obj if you only want the function to run (i.e. you want its side effects) but it either returns no value, or you don't care what its return value is.

Answer 2

JavaScript: The Good Parts was written by Doug Crockford, who has updated his example to look like this:

var obj = (function() {
    var value = 0;

    return {
        increment: function(inc) {
            value += typeof inc === "number" ? inc : 1;
        },
        getValue: function() {
            return value;
        }
    };
}());

So the whole expression is within the brackets.

The idea of the outside brackets, which are not required, is that it makes it clear to developers that this is an intentionally self-executed function. So the value is readability.

Answer 3

There aren't, in this example, any functional differences, but I do think the parentheses make it much more readable. How do you know how it is scoped without the parens? Is it hoisted? This is a brilliant thread on the subject.

ASIDE:

JSLint will complain that "function statements are not invocable. Wrap the whole function invocation in parens." I think most browser parsers not running in strict-mode would generally let it pass, but it's better not to rely on that.