What is Interpolation in AngularJS?

Examples of Interpolation

Invoke a method in the component

String Interpolation is not used to invoke a method in a component, as it is a one-way binding technique used to insert variables into strings. Instead, we can use Property Binding to bind a method to an event in the HTML element, such as the click event. Here is an example of how to bind a method using Property Binding in Angular:

export class MyComponent {
  handleClick() {
    console.log('Button clicked');
  }
}


<button (click)="handleClick()">Click me</button>

In this example, the handleClick method is bound to the click event using Property Binding. When the button is clicked, the handleClick method is called and logs "Button clicked" to the console.

Perform some mathematical operations

export class MathComponent {
  num1: number = 10;
  num2: number = 5;


  add() {
    return this.num1 + this.num2;
  }
}

In this example, we create a component named MathComponent with two variables named num1 and num2, which have initial values of 10 and 5, respectively. We also create a method named add() that adds the values of num1 and num2.

We can use Property Binding to display the result of this method in the component's template.

<div>Result of addition: {{add()}}</div>

In this example, we use String Interpolation to display the result of the add() method.

Bind to an element property

Binding to an element property in Angular sets the value of an element's property dynamically.

Example:

export class MyComponent {
  disabled: boolean = true;
}
<button [disabled]="disabled">Click me</button>

In this example, [disabled] sets the value of the disabled property of the button element to the value of the disabled variable in the component.

Use a template reference variable

Using a template reference variable in Angular allows accessing an element's properties and methods in the component.

Example:

<input #myInput type="text">
<button (click)="logInputValue(myInput.value)">Log input value</button>

In this example, #myInput is the template reference variable for an input element. We can access the value of the input element in the component method logInputValue() by passing myInput.value as a parameter.

Cross-site Scripting or XSS

XSS is a security vulnerability where attackers inject malicious code into a web page viewed by other users. It occurs when a web application does not properly validate user inputs before rendering them to the user's browser.

Attackers can exploit XSS vulnerabilities to steal sensitive user data, such as login credentials. They can also use XSS attacks to redirect users to malicious websites or perform other malicious actions.

For example, an attacker might inject code into an input field that, when rendered, executes malicious code that steals data or takes control of the user's browser.

Properties of Interpolation in Angular

Let's take a look at what interpolation can do in Angular:

• You put {{expression}} in your HTML code to use interpolation.
   
• You can show many different types of things with interpolation, like words, numbers, lists, and more.
   
• Some special things like ++, --, &&, and || won't work with interpolation.
   
• You can only show public or protected things, not private ones.

Implementing Interpolation in Angular with Examples

To use interpolation in Angular, we put our data or expression inside two curly braces like this: {{ expression }}.

Here are some simple examples to help you understand interpolation in Angular. To use interpolation, you need to create an Angular project. When you create a project, you will see a screen that looks like the picture shown.

The app.component.html is the file in which you will write your HTML documents.

Let’s write in an HTML file.

app.component.html

<h2> {{title}} </h2>

To implement interpolation, we will make changes in our app.component.ts file.

import { Component } from '@angular/core';
@Component ({
    selector: 'app-root',
    templateUrl: './app.component.html',
   styleUrls: ['./app.component.css']
})
export class AppComponent {   
   title = "Hello Ninjas";
}

Compile our code using the ng serve command

After successfully compilation, you will see the output as:

Let’s see some more examples:

Let’s write in an HTML file.

app.component.html file

Let’s use operation in an HTML file.

<h2>Welcome to coding Ninjas</h2>
<h2>{{3+3}}</h2>

Output

Let’s call the function through interpolation.

app.component.html file

<h2>{{title}}</h2>
<h2>{{getData()}} </h2>

app.component.ts file

import { Component } from '@angular/core';    
@Component({    
  selector: 'app-root',    
  templateUrl: './app.component.html',    
  styleUrls: ['./app.component.css']    
})    
export class AppComponent {   
  title = "Hello Ninjas";
getData(){
 return "The Data from the Function."
}
}

Output

Let’s check the boolean through the interpolation 

app.component.html file

<h2>{{title}}</h2>
<h2>{{title == "Hello Ninjas"}} </h2>

app.component.ts file

import { Component } from '@angular/core';    
@Component({    
  selector: 'app-root',    
  templateUrl: './app.component.html',    
  styleUrls: ['./app.component.css']    
})    
export class AppComponent {   
  title = "Hello Ninjas";
}
}

Output

Notes on Interpolation

Interpolation is one-way binding

String Interpolation only displays the current value of a variable in a string. It cannot update automatically if the variable changes later. If you change the value of the variable. It won't change the displayed string by itself. You have to update the string manually to show the changes.

Should not change the state of the app

String interpolation is a way to show a variable's value in a string on a webpage. It's important to ensure that the string being displayed does not have the ability to change the state of the application. The state of the app doesn't update automatically if the variable's value changes later. If you change the variable's value, you need to update the string to show the updated value on the webpage.

The expression must result in a string

In String Interpolation, we can add a value or variable to a string. However, we should make sure that the result is always a string. Even if we add a number or boolean, it will be automatically converted into a string before being added to the string.

Works only on Properties & not attributes

String Interpolation is a technique that lets us add variables into strings. It doesn't work for HTML attributes. Attributes are like fixed HTML properties that can't change while the page is running. String Interpolation can only be used with properties and variable values that can change.

String Interpolation vs Property Binding

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Similarities between String Interpolation and Property Binding

String Interpolation and Property Binding are two ways to create dynamic content on a web page. They are similar in how they are written and what they do.

String Interpolation puts the value of a variable into a sentence using ${variable} symbols. For example, console.log(Hello, ${name}!) will show "Hello, John!" if the name value is "John".

Property Binding links the value of a feature of an element to a variable using [] symbols. For example, <input [value]="inputValue"> will connect the value of the inputValue variable to the value feature of the input field.

Both ways make it easy for developers to update content on a web page. It is based on the value of a variable or feature. For example, String Interpolation can be used to make a greeting message with the user's name. While the Property Binding can be used to set an input field value based on a variable.

Difference between String interpolation and Property Binding

Read about Bitwise Operators in C here.

Benefits of the Interpolation

• Interpolation provides seamless integration as it integrates very well with angular features such as pipes, event buildings, directives, etc.
• It also provides a very good readable way to integrate data in the templates.
• Interpolation is one of the ways of data binding, which can be achieved by typescript logic.
• It helps in troubleshooting and debugging. You can easily spot any irregular value of the interpolation values.
• Also, interpolation automatically performs HTML escaping.

Frequently Asked Questions

Why we use string interpolation in Angular?

We use string interpolation in Angular to dynamically render values or expressions in the view. It allows us to display component data in the template and create more dynamic and interactive user interfaces.

Which formula is used for interpolation?

The formula used for interpolation, often called linear interpolation, calculates an estimated value within a range based on known data points. It uses the equation of a straight line to make this estimation.

What is the difference between interpolation and data binding in Angular?

Interpolation is a simpler way of displaying data within text, while data binding is a broader concept that encompasses various methods (including interpolation) to link your component's data to the view (HTML). Interpolation is like a one-way street, showing data in the template, while data binding can be two-way, allowing user changes to update the component's data.

What is the difference between interpolation and template expression?

Interpolation is a specific type of template expression that uses double curly braces {{ }} to embed an expression within text. Template expressions can be more complex calculations or function calls displayed within the template, not limited to just variable values.

What is interpolation in JavaScript?

Interpolation itself isn't a core JavaScript feature, but it's a concept used in frameworks like AngularJS. JavaScript does have template literals (using backticks) that allow embedding expressions within strings, but it's not directly related to AngularJS interpolation.

Conclusion

In this blog, we discussed What is Interpolation in AngularJS? Interpolation in AngularJS is your magic key to weaving data into your webpages. With a sprinkle of double curly braces, you can create dynamic and interactive experiences. Remember, interpolation is a one-way street for displaying data, but it's a powerful tool to get you started.

To learn more concepts of Angular, please refer to our blog.

AngularJS Events.

Angular 8 Interview Questions.

AngularJS References.

AngularJS Form Validation.

AngularJS Tutorial.

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