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in this video i want to introduce you to
react and go over the core concepts i
think every react developer should aim
to learn and master when it came to
putting these concepts together i
selected them based on things you'll
need to build out most of the
functionality that you see in websites
today and things somebody interviewing
you would probably expect you to know
but before we get started i want to
quickly mention my react crash course
that's linked to the video description
in this course you will learn more about
the concepts i mentioned here while
building a fun notes application
so what is react
react is a javascript library for
building out user interfaces when you
look at websites like facebook netflix
and airbnb you're looking at uis built
in react react provides us with a set of
tools and structure for building out
these user interfaces and makes this
process much faster and easier
single page applications with react it's
very common to build out single page
applications so before we get into the
react concepts i want to quickly recap
single page applications and how they
work for anybody that's not familiar
with this concept yet so in traditional
websites we have a template for each
page on our website and return that
template back to the user whenever they
request it with single page applications
however we are working with one single
template and are simply updating all the
components within the dom
personally i think the term single page
application is a bit misleading as it
makes me think there is only one page in
our application when really we're just
using one single template and modifying
all the contents within it
components are what make up the visual
layer of our application and let us
split up our ui into independent
reusable pieces while how you build and
structure your application is completely
up to you traditionally each part of our
ui would be built out separately as its
own component and then added into a
parent component making up the ui for a
specific page a component is a
javascript class or function that
returns back some html well this is
actually something called jsx but more
on that in a second one thing to note
about components is that they can be
nested as deep as you want a component
can hold another component and that
component can hold more components
while i do think you should learn both
class-based components and function
based components at some point with the
addition of react hooks the trend is
shifting more towards using functional
components so if you're trying to decide
which to learn first you can probably
start with functional components
jsx instead of writing traditional html
tags we're going to be using something
called jsx which stands for javascript
xml jsx actually looks a lot like html
with some slight syntax differences and
also gives us some added functionality
take a look at this example and you'll
see how you can use the curly braces to
pass in variables and adding javascript
logic directly into your html
jsx tags are actually very similar to
html tags some notable differences are
things like class declarations which are
written as class name and how event
handlers are added browsers can't
actually read jsx so this code will
actually be run through a compiler and
convert it into traditional html and
javascript code once it's output in the
browser
react router
using a react router is how we can have
multiple pages in a single page
application with react we typically
handle url routing with something called
a router that keeps our ui in sync with
a url because we're not actually
changing pages the router will take care
of rendering out components into the dom
based on the current url
props
when you need to pass data down from one
component to another you can pass it
down as a prop a prop can be passed down
like a function parameter once a prop is
passed down into a component you can now
use that prop anywhere in the child
component
props can be passed down multiple layers
if needed the term for this is called
prop drilling prop drilling can get
messy so we'll talk about some solutions
to this in a minute
state
state is simply a javascript object used
to represent information in or about a
particular component traditionally we
use class based components to set our
state and its values but more modernly
we use react hooks like use state to
create a component state
so let's imagine for a second that we
have a list of notes that we want to
render out in our app we can set an
initial state and then map through that
state and output all that data in our
component we can also update our state
in this example we can set our initial
state as an empty array then we request
some data from our api and update that
state with new data this state update
will trigger our component life cycle
effect which we'll talk about next
the component life cycle
understanding the component life cycle
is a must for every react developer and
is probably one of the most common
interview question for junior developers
a react component has a life cycle that
it goes through and there are three main
phases that we need to know about in
this life cycle each component has a
mounting phase for when it's first being
added to the dom an updating phase for
when we are modifying something and that
component needs to update and an
unmounting phase for when this component
will be removed from the dom with class
components we have these three methods
to take care of these life cycle methods
we have component did mount component
did update and component will unmount
with functional components however we
have a method called use effect that
allows us to work with each part of a
component life cycle react hooks
react hooks only apply to functional
components but due to the popularity of
using function based components hooks
have become essential to learn in this
process
hooks let us add state and other
features without using class based
components before hooks functional
components could not hold any state
hooks are simply functions that allow us
to hook into and manage state
the two most common hooks that you'll
probably use when you first start are
going to be used which lets us set and
update our state in a component and use
effect that is simply a function that
allows us to manage our component life
cycle react gives us a whole list of
built-in hooks along with the ability to
create our own custom hooks
state management
while we can create and manage state
inside of our components there will
likely be a time when we need to create
some form of global state to make data
available across multiple components
think of something like holding data for
a logged in user you may need this user
across multiple components like your
header bar or a profile component and
passing this data down through props may
not be practical especially when this
information is updated somewhere inside
of those components we have several
options to handle this like using the
built-in context api or using a
third-party package like redux and many
others out there with these we are able
to create some form of global state and
use it across multiple components in our
component tree without having to deal
with prop drilling
the virtual dom
at some point in the process of learning
react you will want to have an
understanding of how the virtual dom
works understanding this will help you
understand and make sense of how react
builds and updates our dom and the
complete life cycle of a react component
in short react creates something called
a virtual dom which is a virtual
representation of the real dom when
we're updating our components we're
actually updating the virtual dom and
not the real dom using this method react
can find the most efficient way to
update the real dom by updating only
areas where changes have been made
without having to update the entire dom
the key prop
when it comes to rendering out a list of
data in your components there is one
thing you should be aware of and that is
the key prop each item in a dynamically
rendered list should contain the key
prop or else you'll get this annoying
air in the console
this prop should be unique and helps
react identify which items have been
changed added or removed so react knows
which part of the virtual dom to update
event listeners
handling events with react is very
similar to how we would do this in
traditional javascript with a few
differences in react we camelcase event
names and we pass in the function we
want to call directly in line between
two curly braces so there is no need for
methods like add eventlistener because
our javascript code and html are mixed
together
handling forms with react how we handle
forms is a little bit different from the
traditional method because we are trying
to keep all our information in some form
of state inside of our component
html elements such as input text area
and select typically maintain their own
state and update based on a user's input
with react however we typically add in
event listeners to each field and update
our component state whenever any one of
these inputs change so methods like on
change and on submit would directly
update our state and would be controlled
by our own functions instead of letting
the form handle all of this on its own
conditional rendering there is always a
chance that you will need to render out
some content conditionally depending on
other values inside of your application
think of something like a user's name
inside of a navigation bar depending on
the user's authentication status you
will either display the user's name or
display nothing one way we can go about
handling this is using the logical and
operator we can also use the inline if
else conditional operator if we want to
add in some extra logic in both of these
examples the rendered output will depend
on the conditions we provide
common commands there are three main
commands i want to mention here because
these are commands you will use in every
project we have the create react app
command which creates the boilerplate
files for a react application we have
the start command that starts up our
development server so we can view our
project right away and we have the run
build command that builds a directory
for a production build of our app for
deployment alright so that's my list of
core concepts every react developer
should master don't forget to subscribe
if you enjoyed this video and make sure
to check out the react crash course
linked in the video description if you
want to learn more

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1. Question text
A) Option1
B) Option2
C) Option3
D) Option4
Correct: C
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