Angular: conditional class with *ngClass

Question

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

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

Answer 1

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

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