#19 Understanding Directives | Angular Components & Directives | A Complete Angular Course

Summary

In this lecture, the key concept of Angular directives is explained. Directives are instructions for manipulating the DOM, with three types: component directives (Angular components with templates), attribute directives (modifying the appearance or behavior of elements), and structural directives (adding or removing DOM elements). Examples include built-in directives like *ngIf, *ngFor, and custom attribute directives like changing background colors. The lecture emphasizes how directives are created using TypeScript classes and decorated with Angular's @Directive decorator. Future lessons will explore built-in directives in greater detail.

Takeaways

• 📦 Components are the basic building blocks of any Angular application.
• 📋 A directive is an instruction to the DOM, used to manipulate it in Angular.
• 🏗️ Directives can change the appearance, behavior, or layout of DOM elements.
• 📑 Angular directives are classified into three types: component directive, attribute directive, and structural directive.
• 🖼️ Component directives are Angular components, which come with a template and manipulate the DOM by rendering view templates.
• 🎨 Attribute directives change the appearance or behavior of a DOM element, like changing the background color, without adding or removing elements.
• 🛠️ Structural directives manipulate the DOM layout by adding or removing elements, using built-in directives like `ngIf`, `ngFor`, and `ngSwitch`.
• 💡 Structural directives are prefixed with an asterisk (*) to indicate DOM manipulation.
• 🏷️ Directives typically use attribute selectors but can also be configured as CSS class, HTML tag, or ID selectors.
• 🔧 A directive is essentially a TypeScript class decorated with a `@Directive` decorator to make it function as a directive in Angular.

Q & A

What is a directive in Angular?

A directive in Angular is an instruction to the DOM, used to manipulate its behavior, appearance, or layout. Directives help Angular extend HTML and are a fundamental part of the framework.

What are the three types of directives in Angular?

The three types of directives in Angular are component directives, attribute directives, and structural directives.

How is a component directive different from other directives?

A component directive is a directive with a template, meaning it renders a view in the DOM. Other directives like attribute and structural directives do not have templates and manipulate DOM elements in different ways.

What is the purpose of an attribute directive?

An attribute directive is used to change the appearance or behavior of a DOM element. It does not add or remove elements from the DOM but modifies the way an element behaves or looks.

Can you give an example of an attribute directive?

An example of an attribute directive is a custom directive that changes the background color of an element, like `changeToGreen`. Angular also provides built-in attribute directives like `ngStyle` and `ngClass`.

What is a structural directive, and how does it differ from an attribute directive?

A structural directive can change the layout of the DOM by adding or removing elements, unlike attribute directives which only modify existing elements. Examples of structural directives include `ngIf`, `ngFor`, and `ngSwitch`.

Why is an asterisk (*) used before structural directives in Angular?

The asterisk before a structural directive, like `ngIf`, tells Angular that the directive will manipulate the DOM by adding or removing elements.

How is the selector of a directive different from that of a component?

While a component's selector is typically used like an HTML tag, a directive’s selector is often used as an HTML attribute. However, both can also be configured to use CSS class selectors, tag selectors, or ID selectors.

What is the decorator used to define a directive in Angular?

The `@Directive` decorator is used to define a directive in Angular. This decorator is applied to a TypeScript class, turning it into a directive.

How do structural directives manipulate the DOM?

Structural directives manipulate the DOM by adding or removing elements based on specific conditions. For example, `ngIf` can add or remove elements based on a true or false condition.

Outlines

00:00

📚 Introduction to Angular Components and Directives

In this section, the focus is on recapping the fundamental concepts of Angular components and directives. It explains that components are the basic building blocks of any Angular application and also introduces directives as key elements used to manipulate the DOM (Document Object Model). The speaker emphasizes the three types of directives: component directives, attribute directives, and structural directives, explaining how they extend HTML functionalities by controlling the behavior, appearance, or layout of DOM elements.

05:02

🖼️ Understanding Component Directives

This section delves into component directives, which are synonymous with Angular components. It explains that a component is essentially a directive with a template. The section highlights that when a component's selector is used, Angular is instructed to render the component's template and its logic at that location in the DOM. Although components manipulate the DOM, they differ from other directives because they come with a template, while others do not.

🎨 Attribute Directives: Manipulating DOM Element Appearance

Here, attribute directives are discussed in detail, explaining their role in changing the appearance or behavior of DOM elements without rendering or removing elements from the page. A custom directive example, 'changeToGreen', is used to illustrate how attribute directives work. The speaker also introduces built-in attribute directives such as 'ngStyle' and 'ngClass' for modifying the appearance of web page elements conditionally.

🧩 Structural Directives: Modifying the DOM Layout

This section introduces structural directives, which have the ability to change the DOM layout by adding or removing elements. Examples of built-in structural directives like 'ngIf', 'ngFor', and 'ngSwitch' are provided, and the significance of the asterisk (*) before structural directives is explained. This symbol indicates that the directive will manipulate the DOM, usually by adding or removing elements.

📝 Directive Selectors in Angular

This paragraph explains how directive selectors are configured, comparing them to component selectors. It describes the different ways a directive selector can be used: as an HTML tag, an attribute, a CSS class, or even an ID selector. However, the default and most common way to use a directive selector is as an HTML attribute. The speaker highlights that this flexibility allows directives to influence the DOM in various ways.

🏗️ Creating a Custom Attribute Directive

This section explains how to create a custom directive in Angular using TypeScript. A step-by-step example of the 'changeToGreen' directive is given, explaining how to create a directive class and use the '@Directive' decorator to define the selector. The explanation emphasizes that using square brackets in the selector means it will be applied as an HTML attribute, modifying the behavior or appearance of the element.

👨‍🏫 Conclusion and Next Steps

The final section summarizes the key takeaways on Angular directives, highlighting their importance in manipulating the DOM. The speaker mentions that upcoming lectures will cover built-in directives in more detail. The video concludes with an invitation to ask questions and a thank-you note to the viewers.

Keywords

💡Component

In Angular, a component is a fundamental building block used to create and manage different parts of an application. Components define the behavior and appearance of a particular view and contain both the HTML template and the logic, making them reusable across the app. The script highlights that components are directives with templates, meaning they provide specific instructions to Angular on how to render views.

💡Directive

A directive in Angular is an instruction that manipulates the DOM (Document Object Model), controlling how elements appear or behave. Directives extend HTML, allowing developers to change the layout or add dynamic behavior. The video mentions three types of directives: component, attribute, and structural, each with different roles in interacting with the DOM elements.

💡Attribute Directive

Attribute directives are used to modify the appearance or behavior of a DOM element, like adding or changing CSS styles. Unlike component directives, they do not have templates. An example provided in the script is the 'changeToGreen' directive, which changes an element's background color. Built-in attribute directives like 'ngStyle' and 'ngClass' are used to style webpage elements dynamically.

💡Structural Directive

Structural directives in Angular modify the DOM layout by adding or removing elements. They are used for conditional rendering and list iteration, allowing developers to create dynamic views based on conditions or data collections. Examples in the script include built-in structural directives like 'ngIf' and 'ngFor', which alter the visibility and presence of elements on the webpage.

💡Template

A template in Angular refers to the HTML that defines the structure and layout of the view. When a component is used, Angular uses its template to render the content in the DOM. The script emphasizes that components are directives with templates, unlike other directives that don't render HTML themselves but modify existing elements.

💡Selector

A selector in Angular is a key part of defining how a directive or component can be used in a template. It determines where Angular should insert a component or directive. In the case of components, selectors are often used as HTML tags, while for directives, they are used like attributes. The script mentions different types of selectors, such as CSS class, attribute, HTML tag, or even ID selectors.

💡ngIf

'ngIf' is a built-in structural directive used to conditionally add or remove elements from the DOM based on a boolean expression. If the expression evaluates to true, the element is rendered; otherwise, it is not. The script discusses 'ngIf' as an example of how Angular can manipulate the layout based on conditions.

💡ngStyle

'ngStyle' is a built-in attribute directive that allows developers to set inline CSS styles dynamically on an HTML element. It is used to modify the appearance of elements conditionally, making the view responsive to different data states. The script mentions that 'ngStyle' helps in changing the style of elements without affecting the DOM structure.

💡Decorator

A decorator in Angular is used to attach metadata to classes, making them identifiable as specific parts of an application, such as components or directives. For directives, the 'Directive' decorator is used, which tells Angular that the class is a directive and defines its selector. The script describes how the decorator is applied to TypeScript classes to create directives.

💡Metadata Object

A metadata object in Angular provides additional information to Angular about how a directive or component should be processed, instantiated, and used at runtime. For directives, metadata includes properties like 'selector', which defines where and how the directive should be applied. In the script, metadata is associated with the 'Directive' decorator to specify directive properties.

Highlights

Components are the basic building blocks of any Angular application.

Directives in Angular are used to manipulate the DOM and extend HTML.

Angular has three types of directives: component directives, attribute directives, and structural directives.

A component directive is an Angular component that includes a template.

Component directives instruct Angular to render the view template of a component at the place where its selector is used.

Attribute directives modify the appearance or behavior of DOM elements without adding or removing elements.

Examples of built-in attribute directives include 'ngStyle' and 'ngClass,' which can be used to change the appearance of an element.

Structural directives manipulate the DOM layout by adding or removing DOM elements.

Built-in structural directives include 'ngIf,' 'ngFor,' and 'ngSwitch.'

Structural directives are preceded by an asterisk (*) to indicate that they will modify the DOM by adding or removing elements.

Directives are typically added using attribute selectors, but they can also use CSS class selectors or HTML tag selectors.

A directive in Angular is a TypeScript class decorated with the '@Directive' decorator.

To use an attribute directive, wrap its selector in square brackets so it behaves like an HTML attribute.

Structural and attribute directives differ in that structural directives add or remove elements from the DOM, while attribute directives only change appearance or behavior.

The upcoming lectures will focus on built-in Angular directives like 'ngIf' and 'ngFor.'

Transcripts

so far in this course we have learned

about angular components in great detail

we learned that components are the basic

building block of any angular

application and we also learned how to

create and use a component

another key feature of angular is its

directives and in this lecture we will

learn what is a directive and what is

its importance

so basically a directive is an

instruction to the Dom in simple words

we use directives to manipulate the Dom

using directives we tell angular how the

Dom element should behave or look like

and also which term element to add to

the web page and which one to not add

you can change the Dom elements

appearance Behavior or layout using

directives they simply help you extend

HTML in some way

directives in angular can be classified

into three types component directive

attribute directive and structural

directive

a component directive is nothing but an

angular component we learned and used

angular component in our previous

lectures so this component directive is

that angular component okay so component

directive is nothing but components in

angular so a component is also a

directive but it is a directive with a

template components are also a kind of

instruction to the Dom wherever we use a

component there we instruct angular to

render The View template of that

component

right and since we are manipulating the

Dom when we are using a component it is

also a directive but again it is a

directive with a template other types of

directives do not have a template

so once we place the selector of our

component somewhere in the template at

this point of time we are instructing

angular to add the content of our

components view template and the

business logic of the typescript code in

that place where we have used the

selector of that component

so this was our instruction to angular

to render The View template of that

component at that place where we use the

selector

okay so keep in mind that components are

also directives but it is a direct with

a template other types of directives do

not have a template

then attribute directive is another type

of directive using attribute directive

we can change the appearance of behavior

of a Dom element

unlike component directive attribute

directive does not have a template it

does not render anything on the web page

neither it removes anything from the web

page for example we can create a custom

attribute directive called change to

Green for changing the background color

of the web page element to Green

so this can be a custom directive which

we can build and use it on all those web

page elements whose background we want

to change to Green

and as you can see here we are using

that directive like an attribute

now since it is an attribute directive

it is only going to change the behavior

or look of the HTML element on which we

have used it it is not going to add or

remove that element from the web page

we also have built-in attribute

directives like NG style and NG class

which we can use to change the

appearance of a webpage element the

attribute directives can also be applied

conditionally

now we will learn about NG style and NG

class built-in attribute directive in

our coming lectures

next we have structural directive

structural directives can change the

Dome layout by adding and removing Dom

elements it basically manipulates the

Dom by adding or removing Dom elements

from the web page

and just like attribute directive

structural directive also does not have

a template

some of the built-in structural

directives available in angular are ngf

and G4 and NG switch

now one important thing to keep in mind

here is that whenever we use a

structural directive before that

structural directive we use an asterisk

for example here on this development

when we are using this NG if directive

before that directly we are using an S

check this simply tells angular that the

directive which we are using here it is

a structural directive it is going to

manipulate the Dom by adding or removing

Dom elements

again we will talk about structural

directive and these built-in structural

directives in great detail in our coming

lectures

now we typically add directives with

attribute selector but technically the

selector of a directive can be

configured like the selector of a

component

so we have learned about different types

of selectors in angular so we have CSS

class selector we have attribute

selector we have HTML tag selector right

so generally when we use the selector of

a component we use it like an HTML tag

but in case of directive we use the

selector of a directive like in HTML

attribute but technically we can also

use the selector of a directive like a

CSS class or like an HTML tag or even

like an ID selector

but mostly we use directives like an

HTML attribute

now just like a component a directive is

also a typescript class

and this typescript class is decorated

with a directive decorator

so here you see in order to create a

directive first we are creating a

typescript class we are calling it

change to Green and then in order to

make this typescript class A directive

we are decorating it with a directive

decorator and to this add directive

decorator we are passing the metadata

object and there we are setting the

selector

and if you notice we are wrapping the

value of that selector within square

brackets so we have learned that when we

wrap the selector value within square

brackets like this in that case that

selector can only be used like in HTML

attribute we cannot use it like an HTML

tag

so since we are wrapping it within

square brackets we can use this selector

like in HTML attribute

and that's what you will see here so in

this example we are using this change to

Green directive like in HTML attribute

and when we use a directive on an HTML

attribute it changes its appearance or

behavior it might also add or remove

that HTML element from the Dom

that simply depends on whether that

directive is a structural directive or

an attribute directive

so this was a very high level overview

of what is a directive and what do we

use it for in the upcoming lectures we

are going to learn about some of the

built-in directives in angular

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