Angular: conditional class with *ngClass

What is wrong with my Angular code? I am getting the following error:

> Cannot read property 'remove' of undefined at BrowserDomAdapter.removeClass

<ol>
  <li *ngClass="{active: step==='step1'}" (click)="step='step1'">Step1</li>
  <li *ngClass="{active: step==='step2'}" (click)="step='step2'">Step2</li>
  <li *ngClass="{active: step==='step3'}" (click)="step='step3'">Step3</li>
</ol>

Angular version 2+ provides several ways to add classes conditionally:

type one

[class.my_class] = "step === 'step1'"

type two

[ngClass]="{'my_class': step === 'step1'}"

and multiple option:

[ngClass]="{'my_class': step === 'step1', 'my_class2' : step === 'step2' }"

type three

[ngClass]="{1 : 'my_class1', 2 : 'my_class2', 3 : 'my_class4'}[step]"

type four

[ngClass]="step == 'step1' ? 'my_class1' : 'my_class2'"

[ngClass]=... instead of *ngClass.

* is only for the shorthand syntax for structural directives where you can for example use

<div *ngFor="let item of items">{{item}}</div>

instead of the longer equivalent version

<template ngFor let-item [ngForOf]="items">
  <div>{{item}}</div>
</template>

See also https://angular.io/docs/ts/latest/api/common/index/NgClass-directive.html

> ... > ... > ... > ... > ...

See also https://angular.io/docs/ts/latest/guide/template-syntax.html

> >

> > >

Another solution would be using [class.active].

Example :

<ol class="breadcrumb">
    <li [class.active]="step=='step1'" (click)="step='step1'">Step1</li>
</ol>

That's the normal structure for ngClass is:

[ngClass]="{'classname' : condition}"

So in your case, just use it like this...

<ol class="breadcrumb">
  <li [ngClass]="{'active': step==='step1'}" (click)="step='step1'">Step1</li>
  <li [ngClass]="{'active': step==='step2'}" (click)="step='step2'">Step2</li>
  <li [ngClass]="{'active': step==='step3'}" (click)="step='step3'">Step3</li>
</ol>

with the following examples you can use 'IF ELSE'

<p class="{{condition ? 'checkedClass' : 'uncheckedClass'}}">
<p [ngClass]="condition ? 'checkedClass' : 'uncheckedClass'">
<p [ngClass]="[condition ? 'checkedClass' : 'uncheckedClass']">

You can use ngClass to apply the class name both conditionally and not in Angular

For Example

[ngClass]="'someClass'">

Conditional

[ngClass]="{'someClass': property1.isValid}">

Multiple Condition

 [ngClass]="{'someClass': property1.isValid && property2.isValid}">

Method expression

[ngClass]="getSomeClass()"

This method will inside of your component

 getSomeClass(){
        const isValid=this.property1 && this.property2;
        return {someClass1:isValid , someClass2:isValid};
    }

Angular provides multiple ways to add classes conditionally:

First way

active is your class name

[class.active]="step === 'step1'"

Second way

active is your class name

[ngClass]="{'active': step=='step1'}"

Third way

by using ternary operator class1 and class2 is your class name

[ngClass]="(step=='step1')?'class1':'class2'"

You should use something ([ngClass] instead of *ngClass) like that:

<ol class="breadcrumb">
  <li [ngClass]="{active: step==='step1'}" (click)="step='step1; '">Step1</li>
  (...)

In Angular 7.X

The CSS classes are updated as follows, depending on the type of the expression evaluation:

• string - the CSS classes listed in the string (space delimited) are added

• Array - the CSS classes declared as Array elements are added

• Object - keys are CSS classes that get added when the expression given in the value evaluates to a truthy value, otherwise they are removed.

<some-element [ngClass]="'first second'">...</some-element>
    
<some-element [ngClass]="['first', 'second']">...</some-element>
    
<some-element [ngClass]="{'first': true, 'second': true, 'third': false}">...</some-element>
    
<some-element [ngClass]="stringExp|arrayExp|objExp">...</some-element>
    
<some-element [ngClass]="{'class1 class2 class3' : true}">...</some-element>

Additionally, you can add with method function:

In HTML

<div [ngClass]="setClasses()">...</div>

In component.ts

// Set Dynamic Classes
  setClasses() {
    let classes = {
      constantClass: true,
      'conditional-class': this.item.id === 1
    }

    return classes;
  }

to extend MostafaMashayekhi his answer for option two> you can also chain multiple options with a ','

[ngClass]="{'my-class': step=='step1', 'my-class2':step=='step2' }"

Also *ngIf can be used in some of these situations usually combined with a *ngFor

class="mats p" *ngIf="mat=='painted'"

You can use [ngClass] or [class.classname], both will work the same.
[class.my-class]="step==='step1'"

   OR

[ngClass]="{'my-class': step=='step1'}"

Both will work the same!

While I was creating a reactive form, I had to assign 2 types of class on the button. This is how I did it:

<button type="submit" class="btn" [ngClass]="(formGroup.valid)?'btn-info':''" 
[disabled]="!formGroup.valid">Sign in</button>

When the form is valid, button has btn and btn-class (from bootstrap), otherwise just btn class.

Let, YourCondition is your condition or a boolean property, then do like this

[class.yourClass]="YourCondition"

We can make class dynamic by using following syntax. In Angular 2 plus, you can do this in various ways:

[ngClass]="{'active': arrayData.length && arrayData[0]?.booleanProperty}"

[ngClass]="{'active': step}"

[ngClass]="step== 'step1'?'active':''"

[ngClass]="step? 'active' : ''"

This is what worked for me:

[ngClass]="{'active': dashboardComponent.selected_menu == 'profile'}"

ngClass syntax:

[ngClass]="{'classname' : conditionFlag}"

You can use like this:

<ol class="breadcrumb">
  <li [ngClass]="{'active': step==='step1'}" (click)="step='step1'">Step1</li>
  <li [ngClass]="{'active': step==='step2'}" (click)="step='step2'">Step2</li>
  <li [ngClass]="{'active': step==='step3'}" (click)="step='step3'">Step3</li>
</ol>

The directive operates in three different ways, depending on which of three types the expression evaluates to:

1. If the expression evaluates to a string, the string should be one or more space-delimited class names.
2. If the expression evaluates to an object, then for each key-value pair of the object with a truthy value the corresponding key is used as a class name.
3. If the expression evaluates to an array, each element of the array should either be a string as in type 1 or an object as in type 2. This means that you can mix strings and objects together in an array to give you more control over what CSS classes appear. See the code below for an example of this.

    [class.class_one] = "step === 'step1'"

    [ngClass]="{'class_one': step === 'step1'}"

For multiple options:

    [ngClass]="{'class_one': step === 'step1', 'class_two' : step === 'step2' }" 

    [ngClass]="{1 : 'class_one', 2 : 'class_two', 3 : 'class_three'}[step]"

    [ngClass]="step == 'step1' ? 'class_one' : 'class_two'"

Not relevant with [ngClass] directive but I was also getting the same error as

> Cannot read property 'remove' of undefined at...

and I thought to be the error in my [ngClass] condition but it turned out the property I was trying to access in the condition of [ngClass] was not initialized.

Like I had this in my typescript file

element: {type: string};

and In my [ngClass] I was using

[ngClass]="{'active', element.type === 'active'}"

and I was getting the error

> Cannot read property 'type' of undefined at...

and the solution was to fix my property to

element: {type: string} = {type: 'active'};

Hope it helps somebody who is trying to match a condition of a property in [ngClass]

<div class="collapse in " [ngClass]="(active_tab=='assignservice' || active_tab=='manage')?'show':''" id="collapseExampleOrganization" aria-expanded="true" style="">
 <ul> 	 <li class="nav-item" [ngClass]="{'active': active_tab=='manage'}">
<a routerLink="/main/organization/manage" (click)="activemenu('manage')"> <i class="la la-building-o"></i>
<p>Manage</p></a></li> 
<li class="nav-item" [ngClass]="{'active': active_tab=='assignservice'}"><a routerLink="/main/organization/assignservice" (click)="activemenu('assignservice')"><i class="la la-user"></i><p>Add organization</p></a></li>
</ul></div>

Code is good example of ngClass if else condition.

[ngClass]="(active_tab=='assignservice' || active_tab=='manage')?'show':''"

[ngClass]="{'active': active_tab=='assignservice'}"

Try Like this..

Define your class with ''

<ol class="breadcrumb">
    <li *ngClass="{'active': step==='step1'}" (click)="step='step1; '">Step1</li>
    <li *ngClass="{'active': step==='step2'}"  (click)="step='step2'">Step2</li>
    <li *ngClass="{'active': step==='step3'}" (click)="step='step3'">Step3</li>
</ol>

For elseif statement (less comparison) use like that: (For example you compare three statement)

<div [ngClass]="step === 'step1' ? 'class1' : (step === 'step2' ? 'class2' : 'class3')"> {{step}} </div>