Question

Why two same statements are returning different results with just parentheses wrapping one and not the other one?

function foo(bar){
    return !bar;
}(false) ? false : true; // returns true

---

(function foo(bar){
    return !bar;
}(false) ? false : true); // returns false! why?!

Answer 1

function foo(bar){
    return !bar;
}
(false) ? false : true

is like saying:

if(false){
   //false
} else {
   //true
}

your function is not called, and your condition is false, meaning it returns the second statement (which has //true).

---

the second is VERY different

(function foo(bar){
    return !bar;
}
(false) ? false : true)

is like this:

function foo(bar){
    return !bar;
}

var temp = foo(false)

if(temp){
    //false
} else {
    //true
}

you are technically creating a self-executing function immediately invoked function expressions (IFFE) with false as a parameter. whatever it returns is subject to the condition. so:

• you passed false as parameter
• the function returns an inversion, which is true
• the return is evaluated, and since the return is true, it executes the first statement of your condition (which has //false)

---

self-executing functions immediately invoked function expressions (IFFE) commonly have these forms, and are commonly used to form closures (which is out of the scope of this question)

var result = (function(innerParam){
    //function body
}(passedParam));

and

//this form commonly seen in jQuery plugins
var result = (function(innerParam){
    //function body
})(passedParam);