A Complete Overview of JavaScript Events - All You Need To Know
Summary
TLDRIn this informative video, Dom introduces the fundamentals of JavaScript events, ideal for beginners and those seeking a refresher. He covers HTML inline events, the crucial 'addEventListener' function, the JavaScript event object for capturing event details, and the distinction between standard functions and arrow functions in event handling. With practical examples, Dom demonstrates how to respond to user interactions like clicks and provides insights on when to use each function type for clear and effective coding practices.
Takeaways
- 😀 JavaScript events allow you to react to user interactions on a webpage, such as clicks or form submissions.
- 📌 The script introduces four main topics for understanding JavaScript events: HTML inline events, the 'addEventListener' function, the JavaScript event object, and the difference between standard and arrow functions in event handling.
- 🔗 HTML inline events are the simplest form of event handling but can be limiting due to the lack of complexity they can manage within the HTML attributes.
- 🔧 The 'addEventListener' method is a preferred approach for attaching events to elements because it keeps JavaScript separate from HTML, making the code cleaner and more manageable.
- 📚 The JavaScript event object provides detailed information about the event that occurred, such as mouse coordinates and whether modifier keys were pressed during the event.
- 👉 Inline event handlers can quickly become messy and are not recommended for complex projects, where separating JavaScript from HTML is advisable.
- 🛠️ Functions like 'onClick' and 'onMouseOver' can be attached to elements to define actions that should occur when specific events are triggered.
- 🔄 When using 'addEventListener', you can specify the event type and a function to be executed when the event occurs, promoting better organization of code.
- 🎯 The 'this' keyword behaves differently in standard functions and arrow functions within event handlers, with the former referring to the element that triggered the event and the latter to the global object.
- 👨🏫 The video script is aimed at beginners and those with some experience who want to review JavaScript events, emphasizing the importance of understanding the basics for effective web development.
- 🔍 The script suggests that developers should research and understand the various types of events available in JavaScript to effectively use them in their projects.
Q & A
What are JavaScript events, and why are they important?
-JavaScript events allow you to react to specific interactions or occurrences on a web page, such as clicks, form submissions, or mouse movements. They are important because they enable dynamic and interactive user experiences by triggering actions when certain events happen.
What is an inline HTML event in JavaScript, and when might you use it?
-An inline HTML event in JavaScript is an event handler directly placed within the HTML element, such as `onclick="alert('Hello!')"`. It's typically used in beginner tutorials for its simplicity but is not recommended for complex projects due to its limitations in maintainability and functionality.
What is the `addEventListener` function in JavaScript, and why is it preferred over inline events?
-The `addEventListener` function is used to attach an event handler to an element separately from the HTML markup. It is preferred over inline events because it keeps the HTML clean, allows multiple events to be attached to a single element, and provides more flexibility in handling events within the JavaScript code.
How does the `getElementById` function relate to event handling in JavaScript?
-The `getElementById` function is used to select an HTML element by its ID, allowing you to reference that element in your JavaScript code. Once selected, you can attach event handlers, such as using `addEventListener`, to respond to user interactions with that element.
What is the JavaScript event object, and what information does it provide?
-The JavaScript event object, often referred to as `e` or `event`, contains information about the event that just occurred, such as the type of event (e.g., click, mouseover), the position of the mouse, and whether modifier keys like Alt or Ctrl were pressed. This information can be used to make the event handling more dynamic and responsive to user actions.
Why might you use an external function for handling events in JavaScript?
-Using an external function for handling events in JavaScript, rather than defining the function inline, helps keep the code organized and reusable. It allows you to separate the logic from the event attachment, making the code easier to maintain, debug, and extend.
What is the difference between a standard JavaScript function and an arrow function in the context of event handling?
-The main difference between standard JavaScript functions and arrow functions in event handling is how they treat the `this` keyword. In standard functions, `this` refers to the element that triggered the event. In arrow functions, `this` is inherited from the surrounding context, often leading to it referring to the global window object instead of the element.
Why might the `this` keyword behave differently in arrow functions compared to standard functions?
-In arrow functions, the `this` keyword does not bind to the element that triggered the event but instead inherits `this` from the surrounding lexical context. This can lead to unexpected behavior, especially in event handlers, where you might expect `this` to refer to the element the event is bound to.
How can you log the event object to the console in JavaScript, and why would you do this?
-You can log the event object to the console using `console.log(e)` within the event handler function. This is useful for debugging and understanding the properties of the event, such as the mouse coordinates or whether modifier keys were pressed, allowing you to tailor your event handling logic accordingly.
What are some common use cases for the information provided by the event object in JavaScript?
-Common use cases for the event object include determining the position of the mouse during a click event, checking if modifier keys (like Ctrl or Alt) were held down, and accessing the target element that triggered the event. This information can be used to create more responsive and interactive user interfaces.
Outlines
📚 Introduction to JavaScript Events
This paragraph introduces the concept of JavaScript events, explaining their purpose and how they allow developers to respond to user interactions on a webpage. It sets the stage for the video by outlining the topics to be covered, including HTML inline events, the addEventListener function, the JavaScript event object, and the difference between standard functions and arrow functions in the context of event handling. The paragraph emphasizes the importance of events for beginners and experienced developers alike, aiming to provide a comprehensive understanding of how events work in JavaScript.
🔗 HTML Inline Events and Their Limitations
The second paragraph delves into the use of HTML inline events, demonstrating how they can be used to trigger JavaScript actions directly within HTML elements. It provides a practical example using a 'div' element with an 'onclick' event that displays an alert message. The paragraph also touches on the limitations of inline events, such as the inability to handle complex logic within the event attributes, and suggests that separating JavaScript code from HTML using external scripts or files is a better practice for maintainability and scalability.
🎯 The Advantages of addEventListener
This paragraph highlights the preferred method of handling events in JavaScript: the addEventListener function. It contrasts this approach with inline events, showing how addEventListener allows for more complex and modular code. The paragraph includes a step-by-step guide on how to use addEventListener, from selecting the HTML element to defining the event type and the function that will be executed upon the event's occurrence. It also discusses the benefits of externalizing event handling functions and the use of the event object to access details about the event.
📌 Understanding the JavaScript Event Object
The fourth paragraph focuses on the JavaScript event object, which contains information about the event that has occurred. It clarifies the role of the event object in providing details such as mouse position and keyboard state during an event. The paragraph demonstrates how to access the event object by passing it as a parameter to the event handler function and then using it to log information to the console. It also explains the various properties available within the event object that can be useful for different scenarios, depending on the project requirements.
⚔️ Standard Functions vs. Arrow Functions in Event Handling
The final paragraph discusses the difference between standard JavaScript functions and arrow functions when used as event handlers. It provides examples of both function types within the addEventListener method and explains the significance of the 'this' keyword in each context. The paragraph points out that 'this' refers to the element being interacted with in standard functions, whereas in arrow functions, 'this' refers to the global object, which can lead to errors if not handled correctly. The video concludes by emphasizing the importance of choosing the right function type based on the specific needs of the event handling scenario.
Mindmap
Keywords
💡JavaScript Events
💡Inline HTML Events
💡addEventListener
💡Event Object
💡Arrow Functions
💡Standard Functions
💡Event Handling
💡DOM Manipulation
💡Event Properties
💡Function Externalization
💡This Keyword
Highlights
Introduction to JavaScript events for beginners and a recap for experienced developers.
Definition of JavaScript events as a way to react to actions on a webpage.
Explanation of the basic concept of event and action in JavaScript.
Overview of four main topics to be covered in the video: HTML inline events, addEventListener function, JavaScript event object, and the difference between standard and arrow functions in events.
Usage of HTML inline events such as 'onClick' for beginner tutorials.
Limitations of inline event handlers in terms of complexity and maintainability.
Introduction to the 'addEventListener' function as the preferred method for handling events.
Demonstration of adding event listeners to a div element with an 'id' of 'box'.
Explanation of how to use different JavaScript events like 'click' and 'mouseover'.
Advantages of separating JavaScript code from HTML for better organization and scalability.
Example of defining and using an external function with 'addEventListener'.
Introduction to the JavaScript event object 'e' and its role in providing information about the event.
Description of properties within the event object, such as mouse coordinates and key presses.
Difference between standard functions and arrow functions in the context of 'this' keyword usage in event handlers.
Implications of using 'this' in arrow functions versus standard functions and potential errors.
Recommendation to use standard functions when 'this' keyword is needed to refer to the element.
Conclusion summarizing the basics of JavaScript events and the importance of understanding them for web development.
Transcripts
hey guys how you going
my name is dom and today we're going to
be taking a look at the basics of
javascript events okay so today's video
is going to be perfect for people who
are just starting out to learn
javascript or
you've got a bit of experience under
your belt and you just want to get a
recap on how the events work
okay so of course the first question
here is going to be
what exactly are javascript events well
essentially they're going to allow you
to react to when
certain things happen on the page so for
example
when the user clicks on a button i want
for example
a drop down menu to show or another
example might be
when the user clicks on a submit form i
want
some sort of validation to happen so
basically you have the event
and then you have the action so in
today's video
we're going to cover four main topics
around
the events to of course gain an
understanding of how they work
so the first topic covered is going to
be the usage of the very basic
html inline events okay so these
are things like your on click which
you'll see on many beginner
tutorials the second topic covered is
going to be the usage of the add event
listener function and this one here is
arguably the most
important the third topic is going to be
the usage
of the javascript event object and these
ones right here
are going to tell you information about
the event which just occurred
and the last topic is going to be the
difference between a standard javascript
function
and an arrow function when it comes to
the events so
hope you guys enjoy and learn something
from today's video
let's get right into the first topic
here the
inline html events okay so
starting off with the most basic form of
a javascript event
handler okay so right here i've got a
fairly straightforward
html file and we can see right down here
i've got this div with an id of box and
i've applied some
fairly straightforward css styles to
this
box so now we can see in the browser
it's going to look
something like this so if i go back
inside the text editor we can see
inside the actual html for the box
itself we can see
it says on click alert hey
decode so this right here is the most
basic form
of a javascript event and you'll find
this style
on many different beginner tutorials out
there on the web
now of course it's quite
self-explanatory what this does
when i click on the box i want this to
say alert
hey decode so now if i was to go inside
the browser
we can see upon clicking on the box we
of course get hey
decode right there and that is the most
basic form like i said
of a javascript event handler now
of course if you're using a text editor
like visual
studio code if you go inside the actual
div here
and you specify for example o n or just
on we can see there are many different
events to choose from
and of course when doing your own
project you're going to be googling
these things and finding out exactly
what type of event you need to use for
your own
scenarios an example might be the on
mouse over event and essentially it's
going to allow you to react to when the
user
hovers their mouse over the actual div
or the box in this case right here
so for example i can just say alerts
then i can say
something like hover okay
just like that so now if i was to save
this we can
we can see of course we actually have
two event handlers right here
the onmouseover and the on click and of
course that is perfectly fine and valid
to have
so now saving this right here going
inside the browser
we can see if i was to hover over the
actual box we get hover
right there if i was to then click
on the box we also get hey d code so
right there we can see an example of
adding the two events
right there now what is the problem with
this
style of event handler well you can't
actually do
much inside these two
inside these quotes okay so of course
you can do quite a few things inside
here but of course
once your project gets more complex and
you want to do
many different things inside the event
handler
you're kind of restricted as to what you
can do inside here
and it can get very messy quite quickly
so
the better option is going to be to
essentially put all of your javascript
code
inside its own separate you know section
of the page or its own file
and then do your event handling inside
there instead
it makes it much easier to work with and
of course that brings us to
the add event listener function okay so
ad event listener is going to be the
preferred way for you to add events to
your javascript code
and of course your web page so right
here we can see we get a very similar
example
i've got the exact same div with an id
of box but now
i've opened up this script tag right
here and i've specified some javascript
code okay so essentially it's going to
do the exact same thing
and i can show you this right now so
going inside the browser we can see
upon clicking on the box we get right
here hey
d code so now looking at the actual code
itself
we can see in the javascript the first
line of code here is simply grabbing
the actual div from the html so right
here i'm just saying
a new constant or new variable
called box div is equal to
document.getelementbyid and i'm passing
in box right here so
for those of you who don't know
essentially if i pass in box right here
it's going to grab this div and now
essentially this div
refers to this box div right inside the
javascript code
so now i'm just simply saying box div
dot add event listener and i'm passing
through here
the click event so similar to the
previous example
where we had the mouse over you can also
pass in
mouse over inside here and that is also
going to work
like i mentioned earlier there are many
different javascript events to use so
you're going to have to do your own
searching and find out what you need for
each different scenario
but let's go back to the basic click
event right here
after this we're simply specifying a
javascript
function right inside here and i'm
accepting
the event object right there so we're
going to get to this
very shortly but for now we can simply
ignore that
and then going inside the actual
function body itself
i'm then saying alert hey d code so
essentially
we're moving the alert call from
inside the html in the previous example
to
this function right inside here and this
makes it
a lot easier to work with and
essentially
you're going to have a much better time
writing your javascript code
inside the script tag or an external
file
compared to inside the html so of course
we saw
how that one works now what if i was to
instead of specifying the function right
here
we can actually specify it externally so
this right here is another example
of what you might see so if i was to
specify a function
right inside here i can say function
and call this function handle box
click so essentially this function is
going to do the job of handling
the box click so now i can also accept
the event object
as we did earlier and then i can simply
move
the alert code inside here and then
instead of having this function right
here i can instead just say
handle box click just like that and that
is going to give us the exact same
result it is simply just a different way
of writing it
and you might see this example or style
also
so if i was to save this we can see we
get the
exact same result we can click and we
get hey
decode so now we're going to move on to
taking a look
at the event object right here so let's
look at that
right now okay so moving on to the event
object i'm referring to
this e right here now i know this e
confused me quite a bit
when i first started learning javascript
but it's actually very straightforward
in what it actually does
so essentially this e or the event
object
contains information about the event
which has just
occurred in the case of the click event
you can find many different pieces of
information
about that click for example you can see
if the user was holding down the alt
or the control key when the click
occurred or even
the position of the mouse now to gain
access to
the event object you simply pass through
a name
for the event object right here inside
the function now of course
you can call this whatever you want for
example
it doesn't need to be e we can say ev
or we can even say event right here
realistically
we could say absolutely anything like d
code for example
and that is also going to work but it is
a nice convention
to simply use e or ev as the name for
the event
object okay so that being said
we can then reference or use the object
inside the function
by saying e just like this now
right here i'm simply saying console.log
and i'm passing through e
so essentially this console.log is gonna
tell me
information about the actual object
right there
inside the javascript developer console
so now if i was to save this right here
and go
inside the browser i can then using f12
you can toggle the developer tools right
inside here
and you may need to switch to the
console output right up here
to gain access to of course the console
so now
if i was to click on the object we can
see
so on the div we can see right here we
get the mouse
event inside the console right here and
notice how it says
mouse events there are many different
event
objects in javascript because of course
this one right here
was a click event a click event relates
to the mouse so of course we get the
mouse event
there is also the keyboard event for
example
so now going inside the actual object
itself we can see
there are many different properties
related to
the event which has just occurred for
example
we gain access to the client x and the
client y
and these are just the the mouse
coordinates
when the click occurred we can see we
get 108
and 80 right inside here if i was to
click
again this time in the top left corner
we can see the client x and the client y
are much lower at 10 and 10.
we also gain access to things like the
control key
and the alt key which of course tell you
if the alt or control key were pressed
or held down when the click occurred for
example we can see now
the control key is set to false but if i
was to hold the control key
and click again we get right inside here
control key
sets a true so of course depending on
your own
scenario or use case you're gonna find
these properties useful okay so of
course
it's gonna depend on your own project
what you're doing
you may not need to use any of these
properties and that's perfectly fine but
in many cases you may need to gain
access to these different
information regarding the event to of
course do
different things okay so let's let's
move on now to
the usage of the of the arrow functions
in comparison to the standard javascript
functions
okay so moving on to the final part of
today's video and that is going to be
the difference between standard versus
arrow functions
when it comes to your event handlers
okay so right here we can see
i have two examples of the usage of the
add event
listener method okay so right here we
can see
the first example is very similar if not
the same in fact it is the same
as our previous examples we're simply
saying function and then of course
taking through the event object and then
we're simply saying right down here
console.log and i'm logging out the
value
of this keyword if you don't know what
this keyword refers to
that is perfectly fine this is still
going to make sense
in the second example this one right
here is probably
one of the more modern ways to write
your javascript event
handlers and this one uses an arrow
function
as we can see right here so these serve
a very similar purpose
and they do basically the exact same
thing it's simply just
a different way of writing out a
javascript function
this one is standard and this one is an
arrow function
now we can see i'm also logging out the
value
of the this keyword so now if i was to
save this right here
go inside the browser then click on the
div we can see
we get our two outputs right there
as we can see in the case of the first
example with the standard function
this refers to or this keyword refers to
the actual box itself so basically if i
go back inside here
in this case this refers to the exact
same thing
as box div right there and that is for
standard functions
when it comes to your arrow function
this refers to
the whole window global object itself
so the reason why i pointed this out is
because
of course if you run into errors where
you know certain things are defined or
you know certain things aren't working
just watch out for cases where you may
be using an
arrow function but then using this
keyword always make sure if using this
keyword right here
you want to make sure you use the
standard javascript function
instead of the arrow functions right
down here
if you want to learn more about the
arrow functions in javascript
i've got a whole video dedicated to that
so you can watch that too
if you like and that is the basics of
javascript
events thanks for watching guys and i'll
see you in the next
video
Посмотреть больше похожих видео
How Events Work in React | Lecture 134 | React.JS 🔥
Handling Events | Mastering React: An In-Depth Zero to Hero Video Series
JavaScript forEach vs. map — When To Use Each and Why
Multiple ways of Fetching Events in React #knowledgekeen
Learn JavaScript Event Listeners In 18 Minutes
Getting Started with Alpine.js
5.0 / 5 (0 votes)