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

Rhett Herring
PLUS
Rhett Herring
Courses Plus Student 11,023 Points
Posted by Rhett Herring
Rhett Herring
Courses Plus Student 11,023 Points

Why do we call the functions with no () ?

Not sure why in the following line

$password.focus(passwordEvent).keyup(passwordEvent).keyup(confirmPasswordEvent).keyup(enableSubmitEvent);

We don't have to call passwordEvent and the other functions to include the '()' like passwordEvent() ???

2 Answers

Thomas Nilsen
Thomas Nilsen
14,957 Points
Thomas Nilsen
Thomas Nilsen
14,957 Points

Here is an additional example to help you understand:

//We add a new function to the Array prototype.
//This basically means you can call this function on arrays.

//Our 'callback' parameter is a function
Array.prototype.customMap = function(callback) {
    var arr = [];

    //'this' - is whoever called the function. i.e. some array
    for (var i = 0; i < this.length; i++) {

        //Here we actually call the 'callback' function 
        //and pass in a number from the array
        arr.push(
            callback(this[i])
        );
    }
    return arr;
}


//This is a function we can pass to our customMap function
function multiply(n) {
    return n * 2;
}

var arr = [1, 2, 3, 4];

//Notice - We're not calling the 'multiply' function here -
//Just passing it in so our customMap function can call it at some point
console.log(arr.customMap(multiply));
Rushabha Jain
Rushabha Jain
Courses Plus Student 132 Points

But for execution of the program we need to give parenthesis after the name of the function. which is not given in -------------------------------------------------------- $password.focus(passwordEvent).keyup(passwordEvent).keyup(confirmPasswordEvent).keyup(enableSubmitEvent)

Michael Hulet
Michael Hulet
47,912 Points
Michael Hulet
Michael Hulet
47,912 Points

In this case, those functions where you don't write the parentheses afterwards are just acting like normal variables. You're not calling them, but you're passing them into those other functions, so those functions (the ones with the parentheses) can potentially modify and call the functions (the ones without the parentheses) you gave them

john larson
john larson
16,594 Points

Michael, that's a good answer, thank you. Now, how will we identify in the future, when we will be using functions as "normal" variables. (Thomas showed a code example but I couldn't relate it to this instance)

Michael Hulet
Michael Hulet
47,912 Points
Michael Hulet
Michael Hulet
47,912 Points

You do that commonly in cases where you want to have another function execute some code after a certain thing has happened, for example when a download finishes. Let's say you have a function that gets data from a server. You don't want to prevent all the other JavaScript from running, so this function will return immediately so the rest of your code can keep running, but it'll call a function you give it when the download finishes. You can write another function that you'll give to the function to download data, like this:

function getData(callback){
    var data = /* All the code it takes to get data */
    callback(newData);
}

function finishedGettingData(newData){
    //Idk update your UI or something with the new data
}

getData(finishedGettingData);

In the case above, finishedGettingData isn't called until getData is done downloading all of its data, but getData knows to call finishedGettingData in specific, because that's what you told it to call

john larson
john larson
16,594 Points

Thanks Michael.