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JavaScript jQuery Basics (2014) Creating a Password Confirmation Form Perfect

Luis Felipe Lino
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.a{fill-rule:evenodd;}techdegree
Luis Felipe Lino
Full Stack JavaScript Techdegree Student 15,707 Points
Posted by Luis Felipe Lino
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Luis Felipe Lino
Full Stack JavaScript Techdegree Student 15,707 Points

Jquery function with or without parentheses

Hi folks, hope you are fine. Well my doubt is:

Why when I call a method within a conditional or within a function I must use parentheses after it, for example:

    function confirmPassword(){
        //hide hint if valid
        if(arePasswordsMatching()){
            $confirm_password.next().hide();
            //else show hint
        }else{
            $confirm_password.next().show();
        }
    };

And when I call a method within a jquery event like focus or keyup I don't need to use paretheses, for example:

$password.focus(passwordEvent).keyup(passwordEvent).keyup(confirmPassword).keyup(enableSubmitForm);

Someone knows the answer?

Sorry about any english mistake ;)

3 Answers

davidschreiter
davidschreiter
15,005 Points

The () will execute the function right then and there.

Without it you are just referring to the function not what it returns.

Sometimes you can pass a function another function for it to use later or you can pass a function the result of another function.

Some functions may be able to handle either and it doesn't matter since it might execute it right away anyways.

The if statement just wants a conditional statement (i.e. true/false) which is what arePasswordsMatching returns.

This is just my understanding of it. I could be off on a few things (or all of it). I'm positive it can be explained better than that. I'm still a bit of a Billy when it comes to programming. Cheers. Good luck.

Marcus Parsons
Marcus Parsons
15,719 Points

Marked as best answer

Robert Mews
Robert Mews
11,540 Points
Robert Mews
Robert Mews
11,540 Points

Hey David,

By saying "The () will execute the function right there" are you saying the "()" at the end of the function name executes the function without having to return?

return functionName();
davidschreiter
davidschreiter
15,005 Points

Hi Robert,

I'm a little confused by your question. I think you may have the return statement mixed up a bit.

The return statement should be inside the function itself. Not all functions have to return something, but any return statement would have to be inside a function. In your example the code would have to exist inside another function. i.e.

function anotherFunction(){

        return functionName();

}

If that's what your referring too, then anotherFunction would return what ever functionName would return.

If functionName didn't have the "()" at the end of it, anotherFunction would just return functionName itself and not execute the code inside functionName.

Then if you stored that result in another variable you could execute the code by using "()" after that variable's name. i.e.

//declaring anotherFunction
function anotherFunction(){  

        return functionName;

}

//execute anotherFunction and store the result in a var
var yetAnotherFunction = anotherFunction();

This is the same as saying yetAnotherFunction equals functionName. Now at this point or any point later we can execute whatever code exists inside functionName by writing "yetAnotherFunction()" or "functionName()".

I hope i helped clear some of it up and not make it even more confusing. Good luck.

Dean Wagman
Dean Wagman
21,591 Points
Dean Wagman
Dean Wagman
21,591 Points

Functions always have parentheses. Those functions you call in jQuery are functions with parentheses. They just have what we call parameters inside of them. Parameters are optional variables you can send to a function, that the function will take and use inside of itself.

For Example:

function startCar(name) {
    console.log("The " + name + " is now on!");
}
startCar("Ferrari");

This code will print out "The Ferrari is now on!"

That is because our function takes a parameter, a variable we send to it, to do things; in this case print its name.

The jQuery functions are accepting parameters that they will use. In this case, we're passing the function another function to run.

Kelvin Zhao
Kelvin Zhao
10,418 Points
Kelvin Zhao
Kelvin Zhao
10,418 Points

I don't think that answers the question that was asked thou. For e.g. in the question above,

$password.focus(passwordEvent);

if I were to use

$password.focus(passwordEvent());

the code wouldn't work. When do we know when to use parentheses, and when we couldn't and should just pass the function name inside?

Max Pedersen
Max Pedersen
7,196 Points
Max Pedersen
Max Pedersen
7,196 Points

David's answer was helpful, though the top answer on this Stack Overflow answer solidified things for me.

If you used the code $password.focus(passwordEvent()), then you are running the passwordEvent() function first (remember that JavaScript processes code from inside parentheses outward), which returns 'undefined.' Running $password.focus(undefined) is not what we're after.

Instead, we want $password.focus() to run the passwordEvent function itself--which, in this case, either hides or shows the hint, instead of returning a value. Hope that helps!

Marcus Parsons
Marcus Parsons
15,719 Points

Max, the reason it is returning undefined is not because the function is being called. It will return undefined regardless of whether it is called immediately or in the future, because there is no return value listed in the function. Anytime a return value isn't specified in the function, it always returns undefined.

To prove that, run these two functions in your console separately and see the return values for each one:

function sayHi(name) {
alert("Hey there " + name + "!");
}
sayHi("Max");

function sayHiReturn(name) {
alert("Hey there " + name + "!");
return "awesome";
}
sayHiReturn("Max");

The first one will return undefined, but the second one will return "awesome" or whatever value you specify to return.

Max Pedersen
Max Pedersen
7,196 Points
Max Pedersen
Max Pedersen
7,196 Points

Hi Marcus,

Thanks for your reply. I agree with everything you've said--I think I was just a bit vague in my original comment. I should have said that in this specific lesson scenario, passwordEvent() will return 'undefined', because, as you said, that specific function in this lesson does not return anything--not that all functions will always return 'undefined'.

Though if that is also incorrect, I'd love to know, as I'm pretty new to this :).

Marcus Parsons
Marcus Parsons
15,719 Points

Any function that does not have a defined return statement will return undefined because return is undefined for that function. This is true for any function. The best way to see this is to construct some of your own functions that either return something or have no return statement like I just did and then copy them into the web console of Chrome or Firefox and see the return value. The return value always comes after everything executes in the code you run. For example, when running the function I posted "sayHiReturn", it will show the return value after the code.