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We're going to begin using the React API to create React elements, which are the smallest building blocks of React apps. Once you have a basic understanding of how React describes and creates elements in your UI, it will be a smoother transition into writing components and JSX, the special syntax React uses to create elements and use components.
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Earlier I mentioned that one
of the benefits of using React
0:00
is that it's component based.
0:03
You create your UI as individual
self contained components.
0:05
But we're not going to start
off by writing components.
0:09
You see, at its core,
React is only a library for creating and
0:11
updating HTML elements in your UI,
that's all it does.
0:16
So to better understand
how React creates UI,
0:19
we're going to begin using
the React API to create React elements.
0:22
Which are the smallest
building blocks of React apps.
0:27
Once you have a basic understanding
of how React describes and
0:30
creates elements in your UI,
0:34
it will be a smoother transition into
understanding components and writing JSX.
0:35
The special syntax React uses to
create elements and use components.
0:40
React provides the createElement
function to create and return elements.
0:45
In app.js, the first thing we'll do
is create a new variable named title,
0:50
then we'll call React.createElement.
0:57
createElement accepts three arguments that
define the element you want to create.
1:01
The first argument is the type
of element you want to create.
1:09
This is usually a string which
represents an HTML element or a tag.
1:13
In this case, I want to create an h1
element so I'll pass it the string h1,
1:18
but this could also be div,
span, p, and so on.
1:22
And for readability I'm placing
each argument on a separate line.
1:26
Now the second argument you pass to
React.createElement is an object
1:30
containing any attribute and
value you want to give the element.
1:35
For example to give the h1 element
in id we can later target with CSS,
1:38
I'll pass an object and inside it write
an id property and set it to main-title.
1:44
You can add as many comma separated
properties as you want to this object.
1:52
For instance, I'll add a title attribute
with title and set it to, this is a title.
1:55
Now, if we're not giving
the element any attributes,
2:03
you can pass it an empty object,
or the value null.
2:07
So the third argument you pass to
React.createElement, is the contents or
2:14
children of the element you're creating.
2:18
For instance any text that will display
between the opening and closing h1 tags.
2:21
It could also be more elements
created by React.createElement or
2:26
it could even be null.
2:30
I'll parse it the string,
My First React Element.
2:32
Now what if the first important details
you should know about React is that React
2:41
does not create actual DOM nodes.
2:46
It's not creating in
the way you would expect.
2:48
For instance the title element we
defined is not a real h1 element.
2:51
It's actually an object
that describes a DOM node.
2:56
It's an object representation
of a DOM node.
2:59
To better demonstrate,
3:01
I'll console.log(title) to
see what output we get.
3:03
Over in the browser console we see
the title react.element recreated,
3:07
represented as an object.
3:12
It has several properties like key,
props, and ref.
3:14
Now the important one is to pay attention
to right now our type and props.
3:18
Notice how the value for
type is h1, the value for
3:24
props is an object containing the id and
title properties we passed to
3:27
createElement,, and the value for
children is the string,
3:32
My First React Element,
which we passed as the third argument.
3:36
So, this React element is
an object describing what you want
3:45
to render to the DOM, or
Display on the Screen.
3:49
For example,
when the h1 get's rendered to the DOM,
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we should have a html
element that looks like this.
3:55
The type property, describes what type of
element we want to create in h1 element.
3:59
Props are like the properties or
4:04
attributes of that element in this case
it will have a title and id attributes.
4:06
And the children property string
value will be turned into a text
4:12
node that reads, My First React Element.
4:17
So this concept is the essence of React.
4:20
The elements that React creates
are actually plain JavaScript objects
4:24
that describe the element you'd
like to display to your UI.
4:29
So how does React render a real DOM node?
4:32
You'll learn about that next.
4:35
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