#16 Property Binding | Angular Components & Directives | A Complete Angular Course

Summary

This lecture delves into the concept of property binding in web development, contrasting it with string interpolation for one-way data binding. It illustrates how property binding is used to assign dynamic values to HTML attributes, as opposed to static data display with string interpolation. Examples provided include binding an image source, enabling/disabling a button based on stock status, and dynamically setting input values. The tutorial also clarifies the difference between HTML attributes and properties, and introduces attribute binding for accessibility and data attributes.

Takeaways

• 📝 String interpolation and property binding are both used for one-way data binding in Angular, passing data from the component class to the view template.
• 🖼 String interpolation is used for displaying data in HTML, such as product titles or names.
• 🔗 Property binding is used to bind a DOM object's property to a value in the component class, allowing dynamic manipulation of the DOM.
• 📸 An example of property binding is setting the 'src' attribute of an image tag to a product's image path stored in the component class.
• 🔄 Property binding can dynamically assign values to HTML attributes, such as enabling or disabling a button based on product stock.
• 🚫 String interpolation cannot be used for certain HTML attributes like 'disabled', 'hidden', and 'checked', where property binding is necessary.
• 🔑 The difference between HTML attributes and properties is that attributes represent initial values and do not change, while properties represent current values and can be dynamic.
• 🛑 For HTML attributes that do not have corresponding properties, such as 'aria-hidden', attribute binding must be used instead of property binding.
• 🔄 An alternative syntax for property binding is using 'bind' followed by the attribute name, like 'bind-value' for input elements.
• 🔧 Property binding is essential for creating interactive and dynamic web applications, allowing for real-time updates to the UI based on data changes.
• 🤔 Understanding the distinction between string interpolation and property binding is crucial for developers to make the right choice in different scenarios in Angular applications.

Q & A

What is the purpose of string interpolation and property binding in Angular?

String interpolation and property binding in Angular are used for one-way data binding, allowing data to be passed from the component class to the view template. String interpolation is typically used for displaying data in HTML, while property binding is used to bind a property of a DOM object to a value in the component class, enabling dynamic manipulation of the DOM.

How does string interpolation differ from property binding in Angular?

String interpolation is used for displaying static or dynamic text within an HTML template, whereas property binding is used to bind a dynamic value to an HTML attribute, allowing for more complex interactions with the DOM elements.

What is an example of when to use string interpolation in Angular?

String interpolation can be used to display the title or name of a product within an HTML template, as it is suitable for showing a piece of data without the need for any further DOM manipulation.

Can property binding be used to manipulate the DOM elements in Angular?

Yes, property binding allows for the manipulation of DOM elements by binding their properties to dynamic values from the component class, enabling actions such as showing or hiding elements, enabling or disabling buttons, and more.

How can you bind an image source to a product object in Angular?

You can create a property within the product object, such as 'pImage', and assign the image path to this property. Then, in the view template, use property binding syntax to bind the 'src' attribute of the 'img' tag to the 'pImage' property of the product object.

What is the syntax for property binding in Angular?

The syntax for property binding in Angular involves wrapping the HTML attribute you want to bind within square brackets and assigning a TypeScript expression within double quotes.

Why can't string interpolation be used for all HTML attributes?

String interpolation cannot be used for certain HTML attributes like 'disabled', 'hidden', and 'checked' because they require a boolean value to enable or disable their functionality, which is not suitable for the text-based output of string interpolation.

What is the alternative syntax to using square brackets for property binding in Angular?

The alternative syntax for property binding in Angular is to use the 'bind' prefix followed by the attribute name, such as 'bindValue' for the 'value' attribute of an input element.

How can you make a button disabled based on the stock status of a product in Angular?

You can use property binding to bind the 'disabled' attribute of the button to a TypeScript expression that checks the 'inStock' property of the product. If 'inStock' is less than or equal to 0, the button will be disabled; otherwise, it will be enabled.

What is the difference between HTML attributes and HTML properties?

HTML attributes represent the initial values set in the markup and are static, while HTML properties represent the current values that can change dynamically as the page loads and scripts execute.

Can you provide an example of using attribute binding in Angular?

Attribute binding can be used for accessibility attributes like 'aria-hidden'. Instead of using square brackets, you would use 'attr.' followed by the attribute name, and assign a TypeScript expression to it within double quotes.

Outlines

00:00

🔗 Introduction to Property Binding

This paragraph introduces the concept of property binding in web development, contrasting it with string interpolation. While string interpolation is used for displaying static data, property binding is employed for one-way data binding to pass dynamic data from a component class to the view template. The lecturer uses an example of displaying a product image to illustrate property binding, explaining the process of assigning a dynamic image path to an HTML image element's 'src' attribute using Angular's property binding syntax.

05:01

🛍️ Manipulating UI with Property Binding

The second paragraph delves into using property binding to manipulate user interface elements dynamically. It discusses enabling and disabling a 'Buy Now' button based on the product's stock status, demonstrating how to use property binding to assign a boolean value to the 'disabled' attribute of a button. The lecturer also clarifies the difference between using string interpolation and property binding, especially for HTML attributes that require dynamic values, such as 'disabled', 'hidden', and 'checked'.

10:01

📝 Advanced Property Binding Techniques

The final paragraph explores advanced property binding techniques, including the use of the 'bind' prefix as an alternative to square brackets for binding properties. It also distinguishes between HTML attributes and properties, explaining that attributes are initial values that do not change, while properties represent current values that can change. The lecturer provides an example of binding an 'aria-hidden' attribute using attribute binding syntax due to its nature as an accessibility attribute. The paragraph concludes with an invitation for questions and well-wishes for the audience.

Keywords

💡String Interpolation

String interpolation is a technique used in programming to embed expressions into a string literal. In the context of this video, it's used for one-way data binding in a component-based framework, allowing data from the component class to be displayed in the view template. The video script illustrates this by showing how to display a product's title or name using string interpolation syntax.

💡Property Binding

Property binding is a concept that enables the binding of a property of a DOM object to a value in the component class, facilitating one-way data binding. Unlike string interpolation, property binding is used to manipulate the DOM or to show dynamic values. The script demonstrates property binding by assigning the 'src' attribute of an image tag to a property in the component class, which holds the path to an image file.

💡One-way Data Binding

One-way data binding is a programming pattern where data flows in a single direction from the model (component class) to the view (template). The video explains that both string interpolation and property binding in the context of web development achieve this pattern. The script provides examples of using these techniques to ensure the view updates when the model changes, but not vice versa.

💡Component Class

In the context of this video, a component class refers to a part of a web application that encapsulates specific functionality and data. The script discusses how data from the component class is passed to the view template using both string interpolation and property binding, highlighting the role of the component class in managing the state and behavior of a web component.

💡View Template

A view template is a file that defines the structure and layout of a user interface in a web application. The video script describes how to use view templates to display data and manipulate the DOM using string interpolation and property binding. The examples given in the script show how the view template is dynamically updated with data from the component class.

💡HTML Attributes

HTML attributes provide additional information about HTML elements and are used to control the element's behavior. The script explains that property binding is particularly useful for assigning dynamic values to certain HTML attributes like 'disabled' on a button element, which cannot be achieved using string interpolation.

💡DOM Manipulation

DOM manipulation refers to the process of altering the structure or content of a webpage dynamically using JavaScript or a web framework. The video script uses property binding as a method for DOM manipulation, showing how to change the 'src' attribute of an image or the 'disabled' state of a button based on data from the component class.

💡TypeScript Expression

A TypeScript expression in the context of this video is a piece of code written in TypeScript that can be evaluated and used within the template. The script shows how TypeScript expressions are used within property binding syntax to assign dynamic values to HTML attributes, such as checking the stock status of a product to enable or disable a button.

💡Attribute Binding

Attribute binding is a specific form of binding used for HTML attributes that do not correspond to properties. The script explains the difference between HTML attributes and properties, and demonstrates attribute binding by showing how to bind the 'aria-hidden' attribute using the 'attr.' prefix instead of square brackets.

💡Data Binding

Data binding is a broad term that encompasses various techniques used to synchronize data objects with the user interface. The video script focuses on property binding as a form of data binding, which allows for the dynamic display and manipulation of data within the view template. It is a fundamental concept in modern web development for creating reactive user interfaces.

Highlights

Introduction to string interpolation and property binding for one-way data binding in Angular.

Explanation of the difference between string interpolation and property binding, with examples.

Demonstration of using string interpolation for displaying data in HTML.

Introduction to property binding for binding a DOM object's property to a value in the component class.

Example of using property binding to display a product image by binding the 'src' attribute of an 'img' tag.

Explanation of hardcoding the source path versus using a property in the component class.

Step-by-step guide on adding an image to a product list using Angular's property binding.

Use of property binding syntax for dynamic values in HTML attributes.

Example of enabling and disabling a 'Buy Now' button based on product stock using property binding.

Clarification on when to use property binding over string interpolation for certain HTML attributes like 'disabled'.

Illustration of incorrect use of string interpolation for attributes that require property binding.

Introduction to the concept of attribute binding in Angular.

Explanation of the difference between HTML attributes and properties, and when to use attribute binding.

Demonstration of attribute binding using 'attr.' syntax for accessibility and data attributes.

Alternative method of using 'bind' keyword for property binding instead of square brackets.

Final summary of property binding and attribute binding in Angular for one-way data binding.

Transcripts

in the last lecture we learned about

string interpolation we use string

interpolation to achieve one-way data

binding by passing data from the

component class to its view template now

in this lecture we are going to talk

about property binding we also use

property binding to achieve one-way data

binding by passing data from the

component class to its view template but

the difference between string

interpolation and property binding is

that

in string interpolation we use it for

displaying a piece of data in the HTML

for example displaying the title of a

product or name of the product or

something like that

but we use property binding to bind the

property of a dome object to some value

which we have in the component class

in this way property binding allows us

to show our high Dom element or

manipulate the Dom in some other way

so in this lecture let's go ahead and

let's learn more about property binding

with some examples

again here we have our product list

component.html file and here we have

product list component class

now what we want is here we want to show

an image for this product

so before this paragraph element I'll go

ahead and I'll use image tag

and in there let's go ahead and let's

specify the source tag and to this

Source tag we need to specify the path

of a image file

now in order to save some time here in

the sample files folder I have one image

let me drag it and let's go to vs code

and let me go ahead and let me paste it

inside this assets folder and inside we

have that image folder so let me put it

inside this image folder

okay and we don't need this planet.jpg

file anymore so let me go ahead and let

me delete it

okay and I want to display this product

image

before the product details so for that

we can say it is in assets folder in

there we have the images folder and in

there we have iPhone dot PNG okay so let

me save the changes

and if we go to the web page that image

should be displayed

okay now here what we are doing is we

are hard coding this Source path so we

are hard coding this Source path and

we're assigning to this Source attribute

now instead of doing it like this what

we can do is in our component class we

can create a property or maybe inside

this product object itself we can create

a property let's say p image okay and to

that we can assign that value

so let me go ahead and let me grab that

image path from here I'll cut it

and I'll paste it here and now we want

to use this property of this product

object in our view template

so here either we can use string

interpolation syntax like this and there

we can say product Dot

P image

and if you save the changes if you go

back to the web page

that image is still displayed

so we can also use string interpolation

syntax here but instead of using string

interpolation syntax since here we are

trying to assign some Dynamic value to

an attribute of an HTML element we can

use property binding syntax

so here we will not use string

interpolation syntax instead we will use

property binding syntax and for the

property binding all we have to do is we

have to wrap this attribute within

square brackets like this and then we

can assign a set of double quotes and

inside these double quotes we can write

any typescript expression okay so inside

these double quotes we can write any

typescript expression

here we want to use the P image property

of the product object so we can say

product

dot the image

and that should be it if I save the

changes and if you go back to the web

page that image should still be

displayed there but now we are using

property binding syntax

so here we are binding the property of a

Dom element to a dynamic value a value

from our component class

right

so this is what property binding is

now let's take one more example so after

these product details let's go ahead and

let's add a button element

and there let's say by now

okay and on this button element let's go

ahead and let's add a property called

disabled

and what we want is we want to make this

buy now button disabled If the product

is not in stock

but if the product is in stock in that

case we don't want to make this button

disabled So currently since we have used

this disabled property if you go back to

the web page there you will see we have

this buy now button but it is disabled

okay so what we want is If the product

is in stock we don't want to disable

this button this button should not be

disabled but if the product is not in

stock in that case this buy now button

should be disabled so let's go ahead and

let's do that for that let's go back to

vs code and again here I'm going to use

property binding syntax and for property

binding we wrap the property the HTML

attribute within square brackets and to

that we can assign double quotes and in

there we can write any typescript

expression

now here we are simply going to check if

product in stock is not greater than 0

so I'll paste it here and we'll simply

use a not operator

on this expression so I'll wrap it

within parenthesis like this and I'll

use a not operator

So currently if you go to this product

list component.ts there you will see

that in stock is 0 so if you go to the

web page

at this time the button should be

disabled but if we go back and if we

change this in stock to maybe 10 and if

we save the changes and now if we go

back you will see that that button is

enabled

so you see here we are passing data from

the component class to its view template

and there we are assigning that data to

an HTML property now you might say here

if we can also use string interpolation

then why do we need another feature like

property binding

well that's because we cannot use string

interpolation for all types of HTML

attribute for example in case of this

disabled if I use string interpolation

instead of property binding so if I wrap

this Within

double set of curly braces like this

here it will not work if I save the

changes and if I go to the web page

there you see the button is disabled and

it is not working properly

so for HTML attributes like

disabled hidden and checked

for these three HTML attributes the

string interpolation syntax will not

work in that case you will have to use

property binding syntax

and that's why we have string

interpolation as well as property

binding for one-way data binding when we

want to display some data in the HTML we

use string interpolation but when we

want to assign some Dynamic value to an

HTML attribute there we use property

binding

okay I hope it is clear

so here instead of using string

interpolation syntax let's use property

binding

okay and let's wrap this property this

HTML attribute within square brackets

and now if we go back it should be

working

see button is enabled but if we change

it to 0

if we go back to the web page

now it is disabled

all right

so I hope with these two examples now

you know what is property binding and

how we can use it as I mentioned when we

wrap an HTML attribute within square

brackets and to that when we assign

double quotes inside that double quotes

we can write any typescript expression

let me show you one more example of

property binding so let's go ahead and

let's create an input element

in this input element let's say I want

to have a value property and in this

value I want to show some value but I

want to show that value dynamically

so basically what I want is in the

component I want to have a property

here let me go ahead and let me create a

property and I will call this property

maybe name and let's say John Doe okay

so here we have a name property assigned

with this value John Doe and now we want

to display this value inside the input

element

so here to this value we want to assign

the values stored in this name property

for that again we can use property

binding syntax so what we will do is

we'll wrap this value within square

brackets and then here we can write any

typescript expression here we simply

want to use this name property so I'll

go ahead and I will assign that name

property to this value attribute if I

save the changes if you go back to the

web page now we should also have an

input element and there you will see

that the value is John Doe the value is

stored in this name property

now there is one more thing which you

will not find in many tutorials and that

is instead of using these square

brackets like this what we can also do

is we can use bind before these

attributes for example I can say

bind value and in this way also it

should be working if I save the changes

and if we go back you see still this

input element is assigned with the value

of the name property but now for the

property binding we are not using square

brackets we are using bind

same thing we can do here so instead of

wrapping this disabled attribute within

square brackets I can use

bind

like this and if you go to the web page

button is disabled

let's go back to component cluster let's

change in stock to 10

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

the web page and now the button is

enabled so you can also use

bind instead of square brackets but

using square brackets is more common so

we will use that itself

and here also instead of bind we will

use square brackets

now just like property binding we also

have something called as attribute

binding

now here you can ask what is the

difference between an HTML attribute and

an HTML property the HTML attribute

represents the initial value and it does

not change but a property represents the

current value and it can change for

example we have accessibility attributes

like area level area head and area

expanded area control or we have data

attributes like data ID data name data

value and we also have this call span

which is a table attribute we use it on

table columns so these attributes when

you try to bind them using property

binding you will get an error there you

need to bind them using attribute

binding so let's try to understand what

is that

so on this input element itself let's go

ahead and let's try to use an

accessibility attribute called

area hidden

okay and here let's try to bind it by

wrapping it within square brackets like

this and you see here we are getting an

error and the error says can't bind to

area head and since it is not a known

property okay that means this area

hidden here it is not a property it is

an attribute and for binding attributes

all we have to do is we have to say attr

dot and then the attribute name and then

again Within These double quotes we can

assign any typescript expression to

these attributes

so if you want to perform attribute

binding you can do it something like

this

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