#13 Types of Component Selector | Angular Components & Directives | A Complete Angular Course
Summary
TLDRThis 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
🧑💻 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.
🔧 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.
Mindmap
Keywords
💡Component Selector
💡HTML Tag
💡HTML Attribute
💡CSS Class
💡ID Selector
💡App Component
💡Template
💡Square Brackets
💡Div Element
💡Angular Directive
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
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