#07 What is a Component | Angular Components & Directives| A Complete Angular Course
Summary
TLDRThis lecture provides an introduction to components in Angular, a key feature of the framework for building client-side applications. It explains that an Angular application is built by combining multiple independent components, starting with a root component (often called the app component). The lecture also covers the parent-child relationship between components and demonstrates how to create a component in Angular. Key steps include creating a TypeScript class, decorating it with the @Component decorator, and declaring it in the module file. A simple example of building a header component is shown.
Takeaways
- 📦 Angular is a component-based JavaScript framework used for building client-side applications.
- 🌳 Every Angular application has at least one root component, conventionally named 'App Component', which can contain child components.
- 🧩 A component is a small, reusable piece of a user interface, and Angular applications are built by combining multiple components.
- 📐 Components can be organized independently, such as a header, sidebar, footer, or content area, and then combined to form the overall application interface.
- 🔗 Components can also have nested child components, forming a parent-child relationship, like a navbar component inside a header component.
- 🏗️ To create a component in Angular, follow three steps: create a TypeScript class, decorate it with the @Component decorator, and declare it in the main module file.
- 📑 The @Component decorator is used to define a component, including its selector and template, which specify how the component will render in the DOM.
- 🗂️ Angular components must be registered in the 'declarations' array of the Angular module to be recognized and used by the framework.
- 🔀 Components can be inserted into the root component or other components using their selector (e.g., 'app-header' for a header component).
- 🛠️ The template for a component can be directly defined using the 'template' property or by specifying an external HTML file using 'templateUrl'.
Q & A
What is a component in Angular?
-A component in Angular is a small, reusable piece of a user interface. Components are the building blocks of Angular applications, and each Angular app has at least one component called the root component.
What is the purpose of the root component in an Angular application?
-The root component, often referred to as the 'app component', represents the entire Angular application. It is the parent component that contains all other components and forms the structure of the app.
How can different parts of the user interface be structured in Angular?
-In Angular, the user interface is split into separate components. For example, a web application could have components for the header, navbar, sidebar, main content, and footer. Each of these can be built independently and combined to create the full user interface.
What is the convention for naming a root component in Angular?
-By convention, the root component of an Angular application is named 'app component', although it can be named anything.
How do components form a parent-child relationship in Angular?
-In Angular, components can have a parent-child relationship where the root component (e.g., 'app component') contains child components like the header, navbar, and footer. Similarly, each child component can have its own child components.
What are the three main steps to creating and using a component in Angular?
-The three steps to create and use a component in Angular are: 1) Create a TypeScript class and export it, 2) Decorate the class with the '@Component' decorator, and 3) Declare the component in the main module file.
What is the purpose of the '@Component' decorator in Angular?
-The '@Component' decorator in Angular is used to define a class as a component. It provides metadata, such as the selector and template, that Angular uses to understand how the component should be rendered.
What is a selector in Angular, and how is it used?
-A selector in Angular is a property defined in the '@Component' decorator. It represents the custom HTML tag that will be used to display the component in the template. For example, the selector 'app-header' can be used in HTML as '<app-header></app-header>'.
How can the template of a component be defined?
-The template of a component in Angular can be defined using either the 'template' property (inline HTML within the component) or the 'templateUrl' property (linking to an external HTML file).
How does Angular become aware of a new component?
-Angular becomes aware of a new component when it is declared in the 'declarations' array of the module (typically 'AppModule'). The component also needs to be imported in the module file.
Outlines
📘 Introduction to Angular Components
In this paragraph, the concept of components in Angular is introduced. Components are described as a key feature of Angular, a JavaScript framework used to build client-side applications. The paragraph explains that Angular applications are made up of multiple independent components, which are then combined to form a complex user interface. Every Angular application has at least one root component, typically called the 'app component', which houses other child components. The paragraph emphasizes that Angular applications are essentially structured as a tree of components.
🔍 Breaking Down UI into Components
This paragraph discusses how Angular divides a user interface (UI) into independent components. A simple web application is used as an example, where different parts like the header, navbar, sidebar, footer, and main content area can be built as separate components. These components can also have their own sub-components, which are inserted into their parent components. This modular approach allows developers to work on each UI section independently before combining them into a full application. The app component is highlighted as the root component that ties everything together.
🛠️ Steps to Create an Angular Component
The paragraph outlines the process of creating a new component in Angular. It begins by explaining that a component is essentially a TypeScript class. The steps include creating a class, decorating it with the `@Component` decorator, and specifying key properties like the selector and template. The example walks through creating a 'header' component by first defining its folder structure inside the app folder. It also explains how to name the component and organize the TypeScript file properly, setting up the component to be reused in the application.
📂 Setting Up and Exporting Component Class
Here, the detailed process of creating a TypeScript class for a component is explained. After creating a file for the 'header' component, the class is defined with the 'class' keyword and exported for use in other files. To convert this TypeScript class into a component, the `@Component` decorator is added. This decorator requires importing from Angular's core library and includes important metadata such as the selector and template. The paragraph covers the basic syntax needed to set up the component class and includes an HTML template as part of the view.
🖥️ Declaring Components in the Angular Module
This paragraph focuses on how to make Angular aware of newly created components by declaring them in the module file. The example uses the 'header' component, which needs to be imported into the app module. Once imported, the component must be added to the 'declarations' array so that Angular knows about it and can use it within the application. The process of registering a component within a module is essential for making it functional in an Angular project.
🔗 Using Component Selector in HTML
The paragraph explains how to use a component in the application by referencing its selector in the HTML. For the 'header' component, the selector 'app-header' is used to embed it into the root component's HTML. When this selector is added, the content from the header component’s template, such as an `h3` element displaying the app name ('Ecart'), will appear on the web page. This demonstrates how components interact with the DOM using their defined selectors.
✔️ Component Creation Recap and Error Handling
This section recaps the entire process of creating and using components in Angular. It reiterates the steps: defining a TypeScript class, using the `@Component` decorator, specifying a selector and view template, and registering the component in the module. The paragraph also highlights the importance of having a view template, as missing it can cause errors. Finally, it emphasizes the need to declare components in the module file to ensure they are recognized and usable in the Angular application.
Mindmap
Keywords
💡Component
💡Root Component
💡Child Component
💡Selector
💡Decorator
💡Template
💡Module
💡Declaration
💡Client-Side Application
💡Parent-Child Relationship
Highlights
Angular is a component-based JavaScript framework for building client-side applications.
A component is essentially a small piece of the user interface.
Every Angular application has a root component, commonly referred to as the app component.
Angular applications are structured as a tree of components, which come together to form the user interface.
Developers can split sections of the web application into independent components (e.g., header, footer, sidebar) to work on them separately.
Each component can have child components, like a navbar inside a header component, or individual menu items within a navbar component.
Parent-child relationships exist between components, where the parent can include and control multiple child components.
To create a component, you first need to create a TypeScript class and export it.
You must use the @Component decorator to transform a TypeScript class into a component.
In Angular, components must have a view template, which can be defined inline using the template property or through an external file with templateUrl.
The selector property in a component allows it to be used as a custom HTML tag.
Once a component is created, it must be declared in the module's declarations array for Angular to recognize it.
The root component file (app.component.html) is where the other components, like header or footer, are inserted using their selectors.
After importing and declaring a component, you can use its selector as an HTML element in the template to render its content.
Without a view template, Angular throws an error indicating that the component is missing essential information.
Transcripts
hello and welcome to another lecture of
this complete angular course in this
lecture we are going to learn about
components in angular a component is the
key feature of an angular application
so angular is a component based
JavaScript framework for building
client-side applications we have learned
that we use angular for creating
client-side applications
now we create these client-side
applications with the help of components
a component is basically a small piece
of user interface
when building an angular application
first we build a bunch of components
independent of each other and then we
combine these components together to
build a complex user interface
every angular application has at least
one component which is referred to as
root component and mostly we call this
root component as app component and this
is just a convention you can call your
root component anything but by
convention we always call the root
component of our angular application as
app component this root component
represents the entire application and it
contains other child components so every
angular application is essentially a
tree of components and combining all
these components together makes a
client-side application with angular
let's try to understand what is a
component visually
so here let's say we have a simple web
application and in this web application
we have a header we have the main
content area we have a sidebar and we
have a footer
so while creating this application using
angular we can split each of these UI
paths into separate components and we
can work on them independently for
example we can split this header into a
separate component and we can work on
that component independently
in this header component we have a nav
bar so we can also split that navbar
into a separate component and once that
component is ready we can insert it in
the header component
in the same way if we want each menu
item here in this neighbor we can create
them as a separate component and then we
can insert them into the navbar
component
then we can also have a separate
component for the sidebar and in this
sidebar we are using some sections so we
can have a separate component for each
of these sections and then we can insert
these section components into the
sidebar component
then we can have a separate component
for this main content area and in that
main content area we can have separate
components for these contents and then
we can also have a separate component
for footer
and once we have all these components
built we can combine all these
components together to create a user
interface
so we can say that at the top we will
have our app component app component is
the root component of our angular
application and in this app component we
insert all our other components for
example in this app component we can
insert a component for header a
component for never a component for main
content area a component for footer and
a component for sidebar
then this sidebar component can have its
own child components like popular
courses 1 popular courses 2 popular
courses 3 Etc in the same way the main
content area can have its own child
components like it can have a cover
image it can have the main content it
can have the Subscribe button so we can
insert as many components as we want
inside another component
now in this example this app component
is the root component and it is the
parent of all the components in this
case this app component is the parent
for header component Neva component main
component footer component and sidebar
component
in the same way this main component is
the parent component for this cover
component content component and this
subscribe component so here we have a
parent child relationship between the
components
all right so I hope with these examples
now you understand what is a component
now let's go ahead and let's create a
component
now in order to create and use a
component we need to follow three steps
first we need to create a typescript
class and we need to export it second we
need to decorate that typescript class
with ADD component decorator and finally
in order to use that class as a
component we need to declare it in the
main module file so let's go ahead and
let's do that
here in vs code let's first go to this
Source folder in that Source folder we
have this app folder and this app folder
is our main application folder
in this app folder we have a component
called app component
and this is going to be our root
component okay now whatever application
code we will write we will write it
inside this app folder so for example
let's say I want to create a component
called header now we are going to insert
that header component inside our root
component which in this case is app
component
and since we are going to insert it in
our app component the convention is the
child component should always go inside
the parent component folder in this case
the parent component folder is this app
component folder and we are going to
insert the header component inside the
app component so the header component is
going to be the child component of app
component so we are going to create a
new folder inside this app folder
and here we are going to name this
folder with the name of the component so
I am going to create a header component
so here I will call this folder as
header
now inside this header folder we are
going to create our header component
and keep in mind that a component is
nothing but a typescript class
so inside this header folder we are
going to create a typescript file let me
go ahead and let me create that file and
this file is going to contain the header
component class
so here the convention to name your
component is first you need to specify
the name here we want to call our
component as header then you need to use
Dot and you need to call it component
and since it is going to be a typescript
file we need to specify the extension as
dot TS
okay so first the component name dot
component and then the extension
so this file is going to contain our
component class
okay so file has been created now inside
this file in order to create a component
first we need to create an exporter
class
in order to create a class in typescript
we use class keyword and then we specify
the name for the class and the
convention here is the name for the
class should be the name of the
component in this case we want to call
the component as header and it should be
prefixed with component
okay
so this is how we create a typescript
class now we also want to use this
typescript class in other files so we
also need to export it from here so that
we can import it in other files
now this class here it is a simple
typescript class it is not a component
class
in order to make this class a component
class we need to decorate it with at
component decorator
okay and in order to use this component
decorator we need to import it from
angular slash core Library
so here first we are importing this
component from angular slash code
library and then we are using it
now to this decorator we need to pass
the metadata object
and in there we need to specify few
properties so as you can see here we are
already seeing a red squiggly that means
we have some error here and it says
component is missing a template so as we
have learned earlier every component
must have a view template
okay so here we are going to specify two
properties the first property is going
to be selector
and we are going to call this selector
as app hyphen the component name which
is header so it is a convention that you
call you selector app hyphen and then
the component name
once we have the selector we also need
to specify the view template now in
order to specify the view template there
are two ways we can either use template
property or we can use template URL
property for now we are simply going to
use template property
okay and to this template property we
can assign some string and inside that
string we can write some HTML so here
I'm going to write an HTML let's say I'm
going to write an S3 element there
and in that S3 element I'm going to
specify the name of this application
which is going to be ecart
and that should be it so here I want to
create a very simple component now the
component has been created okay but
angular is not aware about this
component yet
so what we need to do is we need to tell
angular that we have a component called
header component and whenever the
angular application loads it should know
about this component
do that we need to go to our main module
class
and in here we need to declare our
custom component
so here we need to declare the header
component which we have just created
in order to do that first we need to
import this header component
so for that we can use this import
keyword and then what do we want to
import we want to import header
component
okay and we want to import it from
this path so in the app component we
have this header folder and in that
header folder we have this header
component okay here dot TS is not
required
and once we have imported it now we need
to declare it inside this declarations
array so let me go ahead and let me copy
this component and we can declare it
inside this declaration sorry
and now we should be able to use this
header component
so let's go to our app component.html
which is the root component of our
application and in there I am simply
going to use our header component now in
order to use header component we need to
use it selector so what is the selector
we have specified for this header
component it is app header so let's copy
this selector
let's go to app component.html and there
let's use that selector as an HTML
element
and that should be it if I save the
changes and if I go back to the browser
you can see ecut here so this content it
is coming
from our header component
from this view template
so here we have used this template
property in order to specify the view
template for this header component class
so this S3 element is being rendered in
the browser
here okay so this is how we create and
use a component in angular
first we create a typescript class and
in order to make that typescript class a
component class we decorate it with at
component decorator
and then there we need to specify a
selector and a view template if we don't
specify the view template you will see
that we have an error
as you can see we have an error
so let's get it back
so we need to specify the selector and
the view template and then in order to
use this component class in our
application first we need to declare it
so that the angular will know about this
component and to declare it we need to
go to our module class so in this case
we have only one module class this app
module class and there it is decorated
with this NG model decorator and in
there we have this declarations array so
we need to register we need to declare
our component inside this declarations
array
all right so this is all from this
lecture if you have any questions then
feel free to ask it thank you for
listening and have a great day
Посмотреть больше похожих видео
#12 Create Component using Angular CLI | Angular Components & Directives | A Complete Angular Course
Components | Mastering React: An In-Depth Zero to Hero Video Series
#13 Types of Component Selector | Angular Components & Directives | A Complete Angular Course
useContext Hook | Mastering React: An In-Depth Zero to Hero Video Series
#09 Styling View Template | Angular Components & Directives| A Complete Angular Course
#08 View Template of Component | Angular Components & Directives| A Complete Angular Course
5.0 / 5 (0 votes)