#13 Types of Component Selector | Angular Components & Directives | A Complete Angular Course

Summary

This lecture explains how to use Angular component selectors in different ways beyond the typical HTML tag format. It demonstrates using a component selector as an HTML attribute, CSS class, and even an ID. The presenter modifies the 'top-header' component in the 'app.component.html' file to illustrate these concepts, showing how changes in the selector's declaration affect the component's rendering in the web page's DOM.

Takeaways

• 😀 Component selectors can be used like HTML tags, attributes, CSS classes, or IDs.
• 💡 By wrapping the selector in square brackets, it can be used like an HTML attribute instead of a tag.
• 🛠️ Changing the selector usage from an HTML tag to an attribute requires updating the HTML structure accordingly.
• 🔧 Using a component selector as an HTML attribute changes its rendering structure, replacing the element tag with a div containing the component’s template.
• 🎨 A component selector can be used like a CSS class by prefixing it with a dot (.) and adding it to a class attribute.
• 🆔 Component selectors can also be used as IDs by prefixing them with a pound sign (#), then using it in the HTML as an ID.
• 📝 Angular components are typically used as HTML tags, but selectors are employed as attributes when working with Angular directives.
• 📚 The lecture emphasizes understanding the various ways to use selectors before delving into Angular directives.
• 🔄 The script illustrates how to switch between different selector types and revert to the default HTML tag usage.
• 🎯 Attribute selectors are mainly used in Angular directives, which will be covered in more depth in future lessons.

Q & A

What is the default way to use a component's selector in Angular?

The default way to use a component's selector in Angular is like an HTML tag. This means that the selector is used in the template as if it were a standard HTML element.

How can you use a component's selector as an HTML attribute?

To use a component's selector as an HTML attribute, you wrap the selector in square brackets in the component's `@Component` decorator, like `[top-header]`. In the template, you can then apply the selector as an attribute to any HTML element, such as `<div top-header></div>`.

What happens if you try to use a selector as an HTML tag when it's defined as an attribute?

If you try to use a selector as an HTML tag after defining it as an attribute, Angular will throw an error, stating that the selector is not a known element. The selector must be used as an attribute in this case.

How can you change a component's selector to be used as a CSS class?

To use a selector as a CSS class, you prefix the selector with a dot (.) in the `@Component` decorator, like `.top-header`. In the template, you can apply the selector as a class, such as `<div class="top-header"></div>`.

What changes occur in the HTML structure when using a selector as a CSS class?

When using a selector as a CSS class, the component's view template is rendered inside a div with the class applied. The component’s name will no longer appear as an HTML element but as a class attribute.

How can you use a component's selector as an ID in Angular?

To use a selector as an ID, you prefix the selector with a pound sign (#) in the `@Component` decorator, like `#top-header`. In the template, you can apply the selector as an ID, such as `<div id="top-header"></div>`.

In which scenario would you most commonly use a selector as an HTML attribute in Angular?

Selectors are most commonly used as HTML attributes when creating Angular directives. Directives often use attribute selectors to apply specific behavior to existing HTML elements.

Why is using selectors like attributes, classes, or IDs not the common practice for components in Angular?

Using selectors as attributes, classes, or IDs is uncommon for components because components are usually designed to represent self-contained UI elements, making HTML tag selectors the most intuitive and common choice. Attribute selectors are more typical for directives that modify behavior rather than rendering UI elements.

What is the main purpose of the lecture described in the script?

The main purpose of the lecture is to demonstrate how a component's selector in Angular can be used in different ways—such as an HTML tag, an attribute, a CSS class, or an ID—and to explain when and why each type of selector might be used.

What does the lecturer suggest about understanding attribute selectors before discussing directives?

The lecturer suggests that understanding how to use attribute selectors is important before discussing directives, as Angular directives often rely on attribute selectors to apply specific functionality to elements in the DOM.

Outlines

00:00

🧑‍💻 Understanding Component Selectors in Angular

In this section, we explore how to use the selector of an Angular component. Typically, the selector can be applied as an HTML tag, but there are alternative ways to use it, such as an HTML attribute or a CSS class. The example of the 'top header' component is used to illustrate these concepts. Initially, the 'top header' selector is applied like an HTML tag, which renders the component’s view template on the webpage. By inspecting the DOM, the 'top header' is shown as a tag element inside the body. This serves as the foundation before introducing other ways of using the selector.

05:00

🔧 Using Selectors as HTML Attributes

This part of the script explains how to use a component selector as an HTML attribute. By enclosing the selector within square brackets, the script shows how this method changes how the component is rendered. The 'top header' selector is converted from an HTML tag to an HTML attribute, which results in an error when used as a tag, demonstrating that the selector must now be used as an attribute. After modifying the HTML structure to accommodate this, the example shows how the 'top header' component is successfully rendered as an attribute on a div element.

🎨 Applying Component Selectors as CSS Classes

Here, the script shifts focus to using the component selector as a CSS class. By prefixing the selector with a dot (.), the selector is transformed into a class, which can be applied in the HTML like any other CSS class. The example demonstrates how the 'top header' selector can now be assigned as a class to a div element, resulting in the same visual rendering as before, but with the selector applied as a class. The DOM structure shows the 'top header' as a class on the div, and the view template is rendered inside the div.

🆔 Using Selectors as IDs in Angular Components

In this section, the script explains how to use the selector as an ID by prefixing it with a pound sign (#). The 'top header' selector is assigned as an ID in the HTML, and the resulting webpage renders correctly. Upon inspecting the DOM, it shows the 'top header' ID applied to a div element, with the view template of the component rendered inside it. This section helps illustrate how selectors can be applied in various forms, although using selectors as IDs or attributes is not common practice in Angular components.

📚 Common Usage and Conclusion

This final section explains that, while Angular allows selectors to be used as HTML attributes, CSS classes, or IDs, they are most commonly used as HTML tags. The use of attribute selectors is particularly prevalent in Angular directives, which are not covered in detail yet but are mentioned as a future topic. The script concludes by restoring the selector to its default HTML tag usage for the 'top header' component and emphasizes that this form of selector usage is typical for Angular components. The closing remarks encourage asking questions and thank the viewer for following along.

Keywords

💡Component Selector

In Angular, a component selector is the way to define how a component will be used in HTML. It can be used in various forms: as an HTML tag, an HTML attribute, a CSS class, or an ID. In the video, the speaker explains how the selector 'top header' is used as an HTML tag and then demonstrates how to use it as an attribute, a class, and an ID.

💡HTML Tag

An HTML tag is a basic building block of HTML, used to define elements in a webpage. In Angular, component selectors can be used like HTML tags. The video shows how the 'top header' component is used as a custom HTML tag in the app component.

💡HTML Attribute

An HTML attribute provides additional information about an HTML element, usually within the opening tag. In Angular, selectors can also be used as attributes by wrapping them in square brackets. The video explains how the 'top header' selector is used as an attribute to render the component.

💡CSS Class

A CSS class is a styling mechanism in web development, applied to HTML elements to define their appearance. Angular components can have their selectors used as CSS classes by prefixing the selector with a dot (.). The video shows an example where the 'top header' selector is applied as a class to a div element.

💡ID Selector

An ID selector is a unique identifier for HTML elements and is often used in CSS or JavaScript. In Angular, a component selector can be used as an ID by prefixing it with a hash (#). The video demonstrates using 'top header' as an ID selector within a div tag.

💡App Component

The App Component is the root component in Angular applications. It serves as the main container for other components. In the video, the 'top header' component is used within the app component, and its behavior when used as a tag, attribute, class, and ID is explored.

💡Template

In Angular, a template defines the HTML view for a component. The video discusses how the 'top header' component’s template is rendered differently depending on how the selector is used (as a tag, attribute, class, or ID).

💡Square Brackets

Square brackets are used in Angular to define selectors as HTML attributes. They allow the component to be applied directly to elements as attributes rather than tags. In the video, the 'top header' selector is wrapped in square brackets to demonstrate this feature.

💡Div Element

A div element is a common HTML element used to group and structure content on a webpage. In the video, the speaker uses a div element to show how the 'top header' selector can be applied as an attribute, class, and ID, with the view template being rendered inside the div.

💡Angular Directive

An Angular directive is a feature that allows developers to attach custom behavior to elements in the DOM. The video briefly mentions that attribute selectors are often used with directives, highlighting that components generally use selectors as tags, while directives commonly use attributes.

Highlights

The selector of an Angular component can be used like an HTML tag, an attribute, a CSS class, or an ID.

When using the selector as an HTML tag, it is used like a custom HTML element, which renders the view template defined in the component.

Selectors can be transformed into an HTML attribute by wrapping the selector name in square brackets (e.g., [top-header]).

If a selector is used as an attribute, it can no longer be used as an HTML tag, resulting in an error if misused.

To use a selector as a CSS class, prefix it with a dot (e.g., .top-header), and it will apply the component’s view template to the HTML element with that class.

Using a selector as a CSS class allows for more flexibility, making it possible to target multiple elements with the same class.

The selector can also be used as an ID by prefixing it with a pound sign (e.g., #top-header), which applies the component’s view template to the HTML element with that ID.

Selectors used as IDs are typically not recommended due to their unique nature, which can limit reusability and flexibility.

Angular components are most commonly used with their selector as an HTML tag, which is the default approach.

Selectors used as attributes are primarily applied in Angular directives, which will be discussed later in the course.

Directives often employ attribute selectors to add behavior or modify existing HTML elements.

In the case of components, using the selector as an HTML tag is the most readable and maintainable method.

Switching between different types of selectors for components is mostly for understanding or edge cases and is not typically used in standard practice.

Understanding the different ways to use selectors is crucial for understanding how Angular components and directives interact with the DOM.

The lecture emphasizes the importance of using selectors correctly to avoid rendering issues and ensure that components behave as expected.

Transcripts

so far we have seen that we can use the

selector of a component like an HTML tag

so wherever we will use that selector

like an HTML tag there The View template

of that component will be rendered

but we can also use a component selector

in different ways for example we have

already seen that we can use a selector

like an HTML tag

but we can also use a selector like an

HTML attribute or like a CSS class

so in this lecture let's learn how we

can use the selector of a component like

an HTML attribute or like a CSS class

and to understand that let's understand

it using this top header component So

currently if I go to the stop header

component.ts file there we have the stop

header component class and there we have

this selector top header and we are

using this selector in the app component

so if I go to app component.html there

we are using that top header selector

like an HTML tag and if you go to the

web page

and there if I inspect the web page here

let me increase the width of this

developer tool and if I go to this body

section in there we have this approot

and in there you will see we have this

top header and inside that top header we

have the same div which we have

specified in the view template of top

header component

okay

now let's say we want to use this top

header like an HTML attribute instead of

using it like an HTML element like an

HTML tag we want to use it like an HTML

attribute

for that all we have to do is we have to

wrap this value within square brackets

like this

and now this selector cannot be used

anymore like HTML tag now we will have

to use this selector like an HTML

attribute so if I go to the web page now

you will see that we have an error

you can see we have an error top header

is not a known element because now top

header cannot be used anymore like an

HTML element now we need to use it like

an HTML attribute

so let's go to app component.html again

and there we are using it like an HTML

element like an HTML tag we cannot use

it like an HTML tag so what we are going

to do is I'll comment this code here

and in the next line let's go ahead and

let's create a div

and for that div let's specify an

attribute called top header

okay so we can use it like an HTML

attribute now if I save the changes and

if we go back

now you will see that we don't have any

error and our application is working as

expected the top header component is

rendered as it was rendering earlier so

there is no difference in that but now

instead of rendering the top header

component like an HTML element it is

going to render it like an attribute so

if I expand this body section again

and if you go to this approach section

there you will not see any top header

tag anymore now you will see a div tag

and for that div tag you will see that

top header attribute

and inside that div tag The View

template of top header component has

been rendered

okay

so this is how we can use a selector

like an HTML attribute

then we can also use a selector like a

CSS class so let's go back

in order to use a selector like a CSS

class let's first remove these square

brackets from here

so in order to use a selector like a CSS

class all we have to do is we have to

use a DOT

and now we can use this selector like a

CSS class so let's go back to

appcomponent.html

and there I can specify a CSS class here

and to that we can assign

top header like this

let's save the changes let's go back to

the web page

and there you will see that the web page

is rendered as it was rendering earlier

but if I expand the body section here

and if we go to this approot there you

will see we have that div on which we

have used the top header class so if I

expand this on that div we will see we

have a CSS class assigned with top

header and inside that div The View

template of top header component has

been rendered

okay

so in this way we can use a selector

like an HTML element like an HTML

attribute or like a CSS class

now we can also use a selector like an

ID for example

in order to use a selector like an ID

instead of dot we need to use bound sign

and then in the app component.html we

can say

ID equal stop header

so if you go back to the web page

the web page is still rendered but now

let's expand this body section let's go

to this absolute section and in there

you will see

on the div we have this ID called top

header and inside that div The View

template of top header component has

been rendered

okay so this tip is the view template of

top header component so that div has

been rendered here

all right now generally in angular we

don't use a selector like an HTML

attribute or a CSS class or a CSS ID we

mostly used it like an HTML tag

but we use selector as an attribute

mainly in case of angular directives now

we have not talked about angular

directives yet but when we use angular

directive when we create angular

directive there we use selector like an

HTML attribute and at that time we use

attribute selector

but here since it is a component we are

going to use it like an HTML element so

for that we are simply assigning the

value to this selected property without

wrapping it within square brackets or

using a DOT or pound sign before this

value

okay then let's go to this app

component.html let's remove this div

from here

and let's uncomment this code

okay so now we are using the selector

like an HTML tag if we save the changes

if we go back to the web page the

application should still be working but

this time we are using the top header

like an HTML tag

but you will understand the use of

attribute selector when we will talk

about directives and that's why I wanted

to talk about different types of

selectors in this lecture before we talk

about directives

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