ng-class in Angular2

Question

I am developing a test application in angular 2 and I\'m stuck with a problem of adding classes based on list from model.

In Angular 1 one could do:

Answer 1

You must specify CSSClass in directives property of @View decorator. Check out this plunk.

@Component({
    selector: 'app',
})
@View({
    template: '<div [class]="classMap">Class Map</div>',
    directives: [CSSClass]
})
class App {
    constructor() {
        this.classMap = { 'class1': true, 'class2': false };

        setInterval(() => {
            this.classMap.class2 = !this.classMap.class2;
        }, 1000)
    }
}

UPD

CSSClass was renamed to NgClass in alpha-35. See this plunk

@Component({
  selector: 'app',
})
@View({
  directives: [NgClass],
  template: `
    <div [ng-class]="classMap">Class Map</div>
  `,
})
class App { /* ... */ }

Answer 2

Using typescript and Angular 2 beta, ngClass doesn't seem to work. From following the API preview - https://angular.io/docs/ts/latest/api/common/NgClass-directive.html

template: '<div [ngClass]="classMap">Class Map</div>'

The example from Google provides two versions of code (which I assume is Alpha and updated to Beta). The new syntax in the website example doesn't seem to work... any ideas?

@View({
    template: `
        <div class="container questions">
            <div class="row formSection">
                 <h2>
                     <div [ngClass]="completed">completed</div>
                </h2>
                <questionSection></questionSection>
            </div>
        </div>
        `,
        directives: [NgClass, QuestionSection],
})

Answer 3

I was trying to do something similar, I had a list of menu items and wanted to specify a fontawesome class for each item. This is how I made it work. In my typescript component I had this:

    export class AppCmp {
       menuItems = [
         {
           text: 'Editor',
           icon: 'fa fa-pencil'
         },
         {
           text: 'Account',
           icon: 'fa fa-user'
         },
         {
           text: 'Catalog',
           icon: 'fa fa-list'
         }
      ]
    }

Then in my html:

  <div *ngFor="#item of menuItems; #index = index">
        <i [attr.class]="item.icon"></i>
        <span>{{ item.text }}</span>
  </div>

Here is the plunker, https://plnkr.co/edit/PIDRZsc7ZhISNgZzOWuY?p=preview Hope that helps

Answer 4

One more method [ Using Ternary Operator and Interpolation]

(Altough Mark Rajcok stated all possible ngClass methods, but you can couple it with ternary operator and you get else condtions)

---

Template

<div class="hard-coded-class {{classCondition ? 'c1 c2': 'c3 c4'}}">
    Conditional classes using <b>Ternary Operator</b>
</div>

or use ternary operator with ngClass, see how

TS

export class App {
  this.classCondition = false;
}

Result

<div class="hard-coded-class c3 c4">
      Conditional classes using <b>Ternary Operator</b>
</div>

Hope it helps someone.

Answer 5

According to the NgClass API docs, Angular 2 will accept a string, an Array, or an Object/map as the expression to NgClass. Or, of course, you could specify a function that returns one of those.

import {Component, CORE_DIRECTIVES} from 'angular2/angular2'

@Component({
  selector: 'my-app',
  directives: [CORE_DIRECTIVES],
  template: `
    <div>
      <h2>{{title}}</h2>
      <div ngClass="gray-border purple">string of classes</div>
      <div [ngClass]="'gray-border purple'">string of classes</div>
      <div [ngClass]="['gray-border', 'green']">array of classes</div>
      <div [ngClass]="{'gray-border': true, 'blue': true}">object/map of classes</div>
      <button [ngClass]="{active: isActive}" (click)="isActive = !isActive">Click me</button>
    </div>
  `,
  styles: [`
    .gray-border {  border: 1px solid gray; }
    .blue   { color: blue; }
    .green  { color: green; }
    .purple { color: purple; }
    .active { background-color: #f55; }
  `]
})
export class App {
  title = "Angular 2 - NgClass";
  isActive = false;
}

Plunker

If you are passing a literal string, note the two alternative syntaxes:

<div ngClass="gray-border purple">string of classes</div>
<div [ngClass]="'gray-border purple'">string of classes</div>

I believe the first is just syntactic sugar for the second.

And to quote the docs:

While the NgClass directive can interpret expressions evaluating to string, Array or Object, the Object-based version is the most often used and has an advantage of keeping all the CSS class names in a template.