Angular interpolation

Interpolation is all about data binding. In Angular data-binding can be broadly classified into 3 categories

Data Binding	Description
One way data-binding	From Component to View Template
One way data-binding	From View Template to Component
Two way data-binding	From Component to View Template & From View template to Component

In this video, we will discuss the first one way data-binding i.e From Component to View Template. We achieve this using interpolation. We will discuss the rest of the 2 data-binding techniques in our upcoming videos.

One way data-binding - From Component to View Template : To display read-only data on a view template we use one-way data binding technique interpolation. With interpolation, we place the component property name in the view template, enclosed in double curly braces: {{propertyName}}.



In the following example, Angular pulls the value of the firstName property from the component and inserts it between the opening and closing <h1> element.

import { Component } from '@angular/core';

@Component({

    selector: 'my-app',

    template: `

                <h1>{{ firstName }}</h1>

              `

})

export class AppComponent {

    firstName: string = 'Tom';

}

Output : 


It is also possible to concatenate a hard-coded string with the property value

<h1>{{'Name = ' + firstName}}</h1>

The above expression displayes "Name = Tom" in the browser.

You can specify any valid expression in double curly braces. For example you can have 

<h1>{{ 10 + 20 + 30 }}</h1>

The above expression evaluates to 60

The expression that is enclosed in double curly braces is commonly called as Template Expression. This template expression can also be a ternary operator as shown in the example below. Since firstName property has a value 'Tom', we see it in the browser.

import { Component } from '@angular/core';

@Component({

    selector: 'my-app',

    template: `

                <h1>{{firstName ? firstName : 'No name specified'}}</h1>

              `

})

export class AppComponent {

    firstName: string = 'Tom';

}

If we set firstName = null as shown below. The value 'No name specified' is displayed in the browser
firstName: string = null;

You can also use interpolation to set <img> src as shown in the example below.

import { Component } from '@angular/core';

@Component({

    selector: 'my-app',

    template: `<div>

                    <h1>{{pageHeader}}</h1>

                    <img src='{{imagePath}}'/>

                </div>`

})

export class AppComponent {

    pageHeader: string = 'Employee Details';

    imagePath: string = 'http://kansiris.com/images/logo.jpg';

}

Output : 


We can also call class methods using interpolation as shown below.

import { Component } from '@angular/core';

@Component({

    selector: 'my-app',

    template: `<div>

                    <h1>{{'Full Name = ' + getFullName()}}</h1>

                </div>`

})

export class AppComponent {

    firstName: string = 'Tom';

    lastName: string = 'Hopkins';

    getFullName(): string {

        return this.firstName + ' ' + this.lastName;

    }

}

Output : Full Name = Tom Hopkins