All language subtitles for 002 What is React.js__en

[Maximilian Schwarzm�ller] So what is React

or React.js as it's actually called?

And why would we use it?

Well, to answer that first question, what it is,

we can of course visit reactjs.org,

the official React.js webpage.

And there we learn that React is a JavaScript library

for building user interfaces.

That's a nice sentence.

But what exactly does that mean?

Consider an example like Netflix Service,

Netflix website and application.

This application is highly interactive

and runs pretty smoothly when we work with it.

It's easy to use

and we don't have to wait for anything to load,

we have nice transitions.

If we go to the My List page

that transition happens pretty much instantly.

We don't seem to wait for a new page to load here,

and that's all pretty nice.

And here I'm using Netflix in my browser.

So this is a website here.

Now, when we use a service like Netflix,

it might almost feel a bit like a mobile app,

even though I am using the website here.

Because mobile apps give us this

great highly reactive user experience.

From mobile apps where use that we have smooth transition

that it's fun to use that app

and that things happen instantly.

And at least traditionally,

websites didn't always feel like this.

Traditionally in websites, when we, for example,

clicked a link or a button,

our request was sent to a server

and a new HTML page was sent back to the browser

where it then could be displayed.

And therefore, traditionally, websites could feel

a bit clunky,

we might have that latency where we wait

for this new HTML page to load and so on.

And it's this request and response cycle,

which we can break up with JavaScript.

So at this point we don't even need React,

it's just a JavaScript which can help us here.

Because JavaScript is a programming language

that allows us as a developer to run logic in the browser.

And the great thing about that logic in the browser

is that it can do things that manipulate what the user sees.

JavaScript in the browser is able to manipulate

to so-called Dom, the HTML elements

that are rendered onto the screen.

We can manipulate this with JavaScript.

And that allows us to change what the users sees

without fetching a new HTML page.

We don't need to request a new HTML page

just to present something different to the user.

So that's why JavaScript can help us.

And since React is a JavaScript library,

it looks like it can also help us with that.

It might be an extra building block,

and indeed, React.js is a client-side JavaScript library.

It helps us with writing that client-side JavaScript code

and it's all about building modern reactive user interfaces

for websites.

And in this course, you're going to learn

about all the different features and tools React.js has

and gives you that make building complex

user interfaces easy.

But one question remains, why do we need React?

Because at this point we know that JavaScript is helpful,

and I hope I could explain why it is.

But how can React specifically help us,

why might we want React in addition to JavaScript?

For this, I built a simple,

a very simple demo here.

A simple website which has some interactivity,

as you will see in the next lecture.

And in the next lecture, I will show you

how we can build this website

and the interactivity it has with just JavaScript,

and how to code what's then look like with React

in addition to JavaScript.

And that will then make it clear

why using React could be a good idea.