Data Binding in Angular 2

Data binding is a core concept in Angular and allows to define communication between a component and the DOM, making it very easy to define interactive applications without worrying about pushing and pulling data. There are four forms of data binding and they differ in the way the data is flowing:

From the Component to the DOM:

Interpolation: {{ value }}

This adds the value of a property from the component:

<li>Name: {{ user.name }}</li>
<li>Email: {{ user.email }}</li>

Property binding: [property]=”value”

With property binding, the value is passed from the component to the specified property, which can often be a simple html attribute:

<input type="email" [value]="user.email">

Here are two more examples, one that applies a background-color from the value of selectedColor in the component and one that applies a class name if isSelected evaluates to true:

<div [style.background-color]="selectedColor">

<div [class.selected]="isSelected">

From the DOM to the Component:

Event binding: (event)=”function”

When a specific DOM event happens (eg.: click, change, keyup), call the specified specified method in the component. In the example below, the cookBacon() method from the component is called when the button is clicked:

<button (click)="cookBacon()"></button>

Two-way:

Two-way data binding: [(ngModel)]=”value”

Using what’s called the banana in a box syntax, two-way data binding allows to have the data flow both ways. In this example, the user.name data property is used as the value for the input, but if the user changes the value, the component property gets updated automatically to the new value:

<input type="email" [(ngModel)]="user.email">

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