#15 String Interpolation | Angular Components & Directives | A Complete Angular Course
Summary
TLDRThis lecture delves into the concept of data binding in Angular, specifically focusing on one-way data binding and string interpolation. The instructor guides through creating a 'product list' component, demonstrating how to dynamically display product details using properties within the component class. The video showcases transitioning from static HTML to dynamic content by binding properties like product name, price, and color. It further illustrates the use of string interpolation for complex expressions, method calls, and ternary operations to render conditional messages, offering a comprehensive understanding of Angular's data binding capabilities.
Takeaways
- 📚 The lecture provided an overview of data binding, explaining the concept of one-way data binding and its implementation methods.
- 🔍 Two methods for achieving one-way data binding were discussed: string interpolation and property binding.
- 💻 A new Angular component named 'product list' was created using the Angular CLI with the 'ng generate component' command.
- 📝 Initially, the 'product list' component displayed hard-coded values for product details, demonstrating static HTML content.
- 🔑 Dynamic content generation was introduced by creating properties within the 'product list' component class, such as 'name', 'price', and 'color'.
- 🦄 String interpolation was utilized to display the values of these properties in the component's view template using double curly braces.
- 🔢 The script showed how to perform calculations and use TypeScript expressions within the double curly braces for dynamic content.
- 🛍 An example of creating a 'product' object with properties and using it in the view template with string interpolation was given.
- 💡 The use of methods, such as 'get discounted price', within string interpolation to perform calculations and return values was demonstrated.
- 📈 The ability to use TypeScript's built-in methods like 'toFixed' to format numbers within string interpolation was highlighted.
- 📉 The use of the ternary operator within string interpolation to conditionally display messages based on the 'in stock' status of a product was explained.
Q & A
What is the main topic of the lecture?
-The main topic of the lecture is string interpolation in Angular for data binding from the component class to the view template.
What are the two ways to achieve one-way data binding in Angular mentioned in the script?
-The two ways to achieve one-way data binding in Angular are using string interpolation and property binding.
How is a new component created in Angular using the CLI?
-A new component is created in Angular using the Angular CLI with the 'ng generate component' command followed by the component name.
What is the purpose of deleting the spec.ts file in the new component?
-The spec.ts file is often deleted as it contains test code, and the focus of the lecture is on component functionality rather than testing.
What is the selector used for the product list component in the script?
-The selector used for the product list component is 'app-product-list'.
How are static values in the product list component's HTML template replaced with dynamic values?
-Static values are replaced with dynamic values by using properties from the component class within the HTML template through string interpolation.
What is the syntax used for string interpolation in Angular templates?
-The syntax used for string interpolation in Angular templates is '{{ expression }}', where 'expression' can be a property name or a TypeScript expression.
How can an object's properties be accessed within the view template using string interpolation?
-An object's properties can be accessed using the syntax 'object.property' within the double curly braces of string interpolation.
What is the purpose of the 'toFixed' method in the context of the script?
-The 'toFixed' method is used to format numbers to a specified number of decimal places, in this case, to limit the display of the discounted price to two decimal points.
How can a ternary operator be used within string interpolation syntax?
-A ternary operator can be used within string interpolation to conditionally display different messages based on the evaluation of an expression, such as showing 'only X items left' or 'not in stock'.
What does the lecture demonstrate about using methods within string interpolation?
-The lecture demonstrates that you can call a component method within string interpolation to perform calculations or operations, such as getting a discounted price.
Outlines
📝 Introduction to Data Binding and Component Creation
This paragraph introduces the concept of data binding in Angular, explaining one-way data binding and its implementation through string interpolation and property binding. The lecturer demonstrates creating a new component called 'product list' using Angular CLI, setting up its class and template, and initially using hardcoded values for product details in the component's HTML. The focus is on setting up the basic structure and understanding the static HTML content, which will later be replaced with dynamic data binding.
🔗 Implementing String Interpolation for Dynamic Data
The lecturer proceeds to explain how to use string interpolation to dynamically pass data from the component class to the view template. This involves modifying the product list component's TypeScript file to include properties for product details and then updating the HTML template to use these properties with double curly braces for interpolation. The paragraph covers the process of updating the template with dynamic expressions, including handling properties within an object and performing basic arithmetic and string operations within the interpolation syntax.
🛒 Utilizing Object Properties and Calculations in Templates
This section delves into using an object to hold product information and accessing its properties within the view template using string interpolation. The lecturer illustrates how to handle errors when properties are no longer directly available and how to access them through the object's properties. It also covers performing calculations, such as calculating a discounted price based on a percentage, and using TypeScript expressions, including method calls and the use of the 'toFixed' method for formatting numbers, within the interpolation syntax.
📉 Conditional Display with Ternary Operators and Conclusion
The final paragraph introduces the use of ternary operators within string interpolation to conditionally display messages based on the product's stock status. The lecturer adds a property to check the stock and uses the ternary operator to display either the number of items left or a 'not in stock' message. The paragraph concludes with a summary of the lecture's main points, emphasizing the ability to pass data from a component to its view template using string interpolation and inviting questions from the audience.
Mindmap
Keywords
💡Data Binding
💡One-Way Data Binding
💡String Interpolation
💡Property Binding
💡Angular CLI
💡Component Class
💡View Template
💡TypeScript Expression
💡Ternary Operator
💡Discounted Price
Highlights
Introduction to data binding and one-way data binding in Angular.
Explanation of two methods to achieve one-way data binding: string interpolation and property binding.
Demonstration of creating a new component named 'product list' using Angular CLI.
Deletion of the spec.ts file from the newly created component.
Configuration of the product list component with a selector and basic setup.
Creation of a static HTML template for the product list component.
Introduction of dynamic content generation using Angular by creating properties in the component class.
Use of string interpolation to display dynamic data from the component class in the view template.
Example of using a product object with properties to replace hard-coded values in the template.
Explanation of accessing properties of an object using dot notation in string interpolation.
Demonstration of performing calculations within string interpolation syntax.
Inclusion of a discount calculation to display the discounted price of a product.
Introduction of a method to calculate the discounted price and its use in the view template.
Use of the 'toFixed' method to format the discounted price to two decimal points.
Application of the ternary operator within string interpolation for conditional display of product availability.
Final demonstration of displaying dynamic content based on the 'in stock' status of a product.
Conclusion summarizing the lecture on using string interpolation for data binding in Angular.
Transcripts
in the last lecture we had a high level
overview of what is data binding and
there we learned that we can pass data
from the component class to its view
template this is called as one-way data
binding and we can achieve it in two
ways we can achieve it using string
interpolation or we can achieve it using
property binding
so in this lecture we are going to talk
about string interpolation
and before we do that let's first go
ahead and let's create a new component
for that I will open the terminal
and I want to create a component called
product list so to create a component
using angular CLI we can use NG generate
command here we want to generate a
component and we want to call it product
list so inside this product list
component we are going to display all
our products let's press enter and let's
wait for this command to complete
so the command has been executed and if
we go to the app folder now there we
should have one more folder called
product list so this product list is
going to contain the product list
component
again as usual I will delete the spec.ts
file from here
let's go to product list component.ts so
here we have this product list component
class decorated with at component
decorator and there the selector is app
product list so let me go ahead and let
me simply call it product list
all right so this is our product list
component now for this product list
component we also have a view template
so this product list component.html is
its view template inside this what I
want to display is I want to display a
product name so I will keep this
paragraph element and there I will say
name and let's say the product name is I
phone
okay then let's also display the price
let's say price is dollar 999.
then let's also display maybe color
let's say color is matte black
and then let's also add one more
paragraph and there let's display
discounted price
and let's say it is dollar 798
okay so with this let's save the changes
and let's grab the selector of this
product list component
and let's go ahead and let's use it
inside our app component so here I'll
open the appcompetent.html file
and in there let me go ahead and let me
use that selector
let's save the changes let's go to the
web page
and there you will notice that those
details are displayed so it is
displaying the name iPhone price dollar
triple nine color matte black discounted
price 798.
but here if you notice in this HTML in
the product list component.html we are
using the hard-coded values for the
product name product price product color
and discounted price right
basically here we are writing the static
HTML and we have learned that for
writing this static HTML we don't need a
framework like angular
we use a framework like angular to
generate Dynamic contents so here what
we will do is I'll open product list
component.ts file and inside this
product list component class let's go
ahead and let's create some properties
so I will create a name property it is
going to be of type string and to this
let's assign some value let's say maybe
iPhone
then let's also specify a price property
it is going to be of type number
and let's say price is
tripling then we also want to have color
property
and again it is going to be a type
string
and let's say color is red
okay and now we want to use these
properties in the product list
component.html let me go and let me
close this app component.html here
okay so here we have our product list
component class and here we have the
view template for that product list
component
so in the product list component class
we have these three properties name
price and color and we want to use the
value of these properties in product
list component HTML
so here instead of writing iPhone
directly we want to read the value of
this name property and we want to
display its value
so here I will simply call it iPhone 13.
okay so in the view template we want to
use the property of the component class
so here we want to pass data from the
component class to view template right
and for that we can use string
interpolation
so here where we want to use the value
of the name property in the view
template there what we can do is there
we can use a double set of curly braces
like this
and inside that double set of curly
braces we can specify the property name
which we want to use in this case
property name is going to be name
so this expression here it will be
replaced by the value stored in this
name property
okay so earlier it was showing iPhone
now it should show iPhone 13. let's save
the changes let's go back to the web
page
and now you see name of the product is
iPhone 13.
so this is how we use string
interpolation to pass data from
component class in this case we are
passing data from product list component
class to its corresponding view template
which is this product list
component.html
in the view template all we have to do
is we have to use a double set of curly
braces and in there we can write any
typescript expression here we are simply
using a property name but we can write
any typescript expression inside this
double set of curly braces
all right so in the same way instead of
writing the hard-coded price here what I
want is I want to use the price property
so this property so again
here let's go ahead and let's use a
double set of curly braces like this and
inside that let's use the property name
which is price
now some of you might say that I have
added a space before the property name
and a space after the property name is
that mandatory no that is not mandatory
because if you see here here I have not
added any space okay so just for
formatting we can add some space but
these spaces are not required okay
in the same way here we want to use the
color property
okay so if you save the changes now and
if you go to the web page
there the value of those properties
should be rendered as you can see
all right
now instead of having these properties
here like this let's go ahead and let's
create an object here
I'll call it
product
okay and inside this product we will
have a name property for this product
object so let's specify a name for the
product again I will say iPhone 10 or
iPhone x
let's specify price here maybe 789 and
let's specify
color
and let's say color is black
so now we don't have any name price and
color property inside this product list
component now we have a product object
and in that product object we have name
price and color property so how can we
use this product object in our view
template using the string interpolation
syntax
so as you can see since these properties
are now not available inside this
product list component class here we
have some error
and the error says name does not exist
on type product list component in the
same way for the price it will say price
does not exist on type product list
component right so here now we want to
use this product property
and from that product property we want
to extract the name price and color
and again we can access this product
property in our view template using
string interpolation so here instead of
name we can say
product Dot
name
and the error is gone in the same way
here we can say product dot price
and here we can say product dot color so
here we are trying to access the name
property the price property and the
color property of this product object
and this product object is basically a
property of this product list component
class
and this should also work so if I save
the changes and if you go to the web
page
now we have the desired result
as I mentioned inside this double set of
curly braces we can use any typescript
expression
so here you see I'm using this dollar
before this string interpolation syntax
but what I can also do is
inside these double set of curly braces
I can specify a string here the string
is going to contain this dollar and then
I can use Plus
so here we are concatenating this string
with this value
so this value will be first converted to
string and those two strings will be
concatenated
so if I save the changes if we go to the
web page
you see we still have dollar 789 but
this time we have concatenated that
dollar using a string
then inside these double set of curly
braces we can also do some calculation
because as I mentioned we can write any
typescript expression inside this double
set of curly bases
so here let's go ahead and let's specify
a discount for this product so let's say
maybe discount is 8.5 percent
so now what we want is based on this
discount we want to display the
discounted price here
so here again let's use a double set of
curly braces basically the string
interpolation syntax and in there we are
going to write some arithmetic
expression
so here what we want to do is we have
this price on this product objects we
can say product dot price okay and we
want to multiply it with the discount so
we can say product dot discount
and this discount
it is in percentage so we also need to
divide it by 100 so we can say divide by
100.
okay and then it should give us the
discounted price so
on this price on this dollar 789 there
is a discount of 8.5 percent
so now this expression here it should
calculate that discounted price and it
should display it so let's see if the
changes let's go back to the web page
and here you see it is showing that
discounted price
so basically on this price there will be
a discount of these many dollars so we
need to subtract this from the original
price
let's go back and let's do that
so I will wrap it within parenthesis
like this okay and we will subtract it
from the original price so for that we
can say product which is the property
name dot price
minus whatever discount price we have
calculated
let's save the changes let's go back to
the web page
and now we have the discounted price
okay so in this way
inside these double set of curly bases
inside the string interpolation syntax
you can write any typescript expression
even you can call a function inside this
string interpolation syntax
let's actually see that so what I will
do is I will cut this logic from here
and in our component class let's go
ahead and let's create a method to
create a method we can simply provide a
name for the method let's call it get
discounted price
and in the body of this method let's
write our expression
now here in order to access this product
property from within this method here we
need to use this keyword
so inside the method whenever you want
to access a property you will have to
use this keyword in order to access that
property okay so since this property is
not a static property we need to use
this keyword in order to access it
so here also we need to use this keyword
and Here Also let's say
this dot product dot discount
and whatever value this expression will
return
we want to return that value from this
method so let's say return
okay and now we can go ahead and we can
call this function in our view template
so let's go to the view template and
inside the string interpolation syntax
let's go ahead and let's call that
method
okay so when we are calling this method
it is going to return us the discounted
price so basically this expression it is
going to return us the discounted price
and that will be displayed here in place
of this expression let's see that let's
see if the changes let's go back
and we still see the discounted price
here
inside this string interpolation syntax
we can also use typescript inbuilt
methods and properties
for example let's say
here in the discounted price we can see
three decimal points but instead of
showing three decimal points let's say
we only want to show two decimal points
so for that in typescript we have a
method called to fixed
so on this result we can go ahead and we
can use that
to fixed method
and to this two fixed method we need to
pass the number of decimal points which
we want in the result here I want only
two decimal points so I will pass two
and now if we save the changes and if we
go back to the web page
now you see we only have two decimal
points after the decimal
we can also use ternary operator inside
this string interpolation syntax let's
understand that with an example so here
for this product let's add one more
property let's call it in stock
and let's say in stock currently we have
five iPhones
okay now what we want to do is if the
products are in stock that means if the
number of product in stock is greater
than 0 then we want to show a message
only that number of product is left so
let me actually show you that with
example
so again I'll add a paragraph element
here
and there let's use string interpolation
syntax and here let's check if product
which is the property name Dot in stock
if it is greater than 0 here we are
going to use ternary operator so if it
is greater than 0 after the question
mark we will specify a string value
we'll say only and then we'll specify
the in stock value
product dot in stock
items left
okay
but if it is not greater than 0 that
means the product is not in stock in
that case we want to say not in stock
okay with this let's save the changes
let's go to the web page so currently
in stock is 5. if you go to the web page
it should say only five items left
but if I change it to 0
and if you save the changes and if we go
back that it will say not in stock
okay so in this way we can also use
ternary operator within this string
interpolation syntax
all right so in this lecture we learned
how we can pass data from component to
its view template using string
interpolation syntax
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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