Angular 2 [attr.class] overwrites native DOM classes

Question

I have a variable holding my class name string:

classNameB = "class-B";

I want to add this class name to a native DOM element via [attr.class]:

<div class="class-A" [attr.class]='classNameB'></div>

Then, angular overwrites the current DOM class class-A. What has left after element created is something like:

<div class="class-B"></div>

What am I doing wrong here and how to work around on this?

PS: Can I use [ngClass] instead and how?

Answer 1

So I went through some funny situations where I almost ran out of options. Most of the time, I use [ngClass] and it was fine until:

<div class='native-class' [ngClass]='classNameHolder' [ngClass]='{"some-class": isSomeClass}'>

where,

classNameHolder: string = 'class-name-1';
isSomeClass: boolean = true;

I was stuck until I find good use of ngClass:

<div class='native-class' ngClass='{{classNameHolder}} {{isSomeClass ? "some-class" : ""}}></div>

And that's it. This is final option that I've been using from then. Hope it'll help if anyone runs into the same sitation.