Remove or add class in Angular

Question

I have a list and the plugin (dragula) I used, adds certain CSS class on certain action. I am using Angular 5. I want to find out the presence of certain class (

Answer 1

If you want to change all li.myClass, you can do like this:

Note the #questions in the container div.

Component.ts

@ViewChild('questions') questions: any;

questions.nativeElement.querySelectorAll('.myClass').forEach(
  question => {
    question.classList.remove('myClass');
    question.classList.add('newClass');
  }
)

Component.html

<div #questions class="right-height" id ='dest' [dragula]='"second-bag"' [dragulaModel]="questions"> 
       {{ questions.length == 0 ? ' Drag and drop questions here ' : ' '}}
       <li
         #vc 
         data-toggle="tooltip"
         data-placement="bottom"
         title= {{question.questionSentence}}
         class="well dragbox"
         *ngFor="let question of questions; let i = index"
         [attr.data-id]="question.questionId"
         [attr.data-index]="i"
         (click)="addThisQuestionToArray(question,i, $event)"
         [class.active]="isQuestionSelected(question)"
         #myId>
           {{question.questionId}} {{question.questionSentence}}
      </li>
</div>

Answer 2

Here are multiple ways to pass classes

<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>

From Official Docs

Answer 3

The Best and easiest way is : -

If student is null then dissabled else not. Use this in button attribute. If you are using bootstrap theme

[ngClass]="{disabled: (students === null) ? true : false}"

Answer 4

You can use id in your html

<button #namebutton class="btn btn-primary">login</button>

add viewchild in your.ts

@ViewChild('namebutton') namebutton: ElementRef;

create a function that will trigger the event

 actionButton() {
    this.namebutton.nativeElement.classList.add('class-to-add')
    setTimeout(() => {
      this.namebutton.nativeElement.classList.remove('class-to-remove')
    }, 1000);
  }
              

and call the function.

Answer 5

Import ElementRef from angular core and define in constructor then try below code:

Below line of code will give you first occurrence of <p> tag from Component. querySelector gives you first item and querySelectorAll gives you all items from DOM.

import { Component, ElementRef } from "@angular/core";

constructor(private el: ElementRef) {
}

let myTag = this.el.nativeElement.querySelector("p"); // you can select html element by getelementsByClassName also, please use as per your requirement.

Add Class:

if(!myTag.classList.contains('myClass'))
{
    myTag.classList.add('myClass'); 
}

Remove Class:

myTag.classList.remove('myClass');