How can i pass conditional variables in custom directive Angular?

I am trying to pass variable in my custom directive. But this gets false or undefined after load. Please help me to find the issue and guide me where i am wrong.

Custom Directive

import { Directive, ElementRef, Renderer2, AfterViewInit, Input, OnInit } from '@angular/core';

@Directive({
  selector: '[air-btn]'
})
export class AirBtnDirective implements OnInit {

  @Input() small?: boolean;
  @Input() outline?: boolean;

  constructor(private el: ElementRef, private renderer: Renderer2) { }

  classes: string[] = [
    'relative',
    'disabled:opacity-70',
    'disabled:cursor-not-allowed',
    'rounded-lg',
    'hover:opacity-80',
    'transition',
    'w-full',
    this.outline ? 'bg-white' : 'bg-rose-500',
    this.outline ? 'border-black' : 'border-rose-500',
    this.outline ? 'text-black' : 'text-white',
    this.small ? 'text-sm' : 'text-md',
    this.small ? 'py-1' : 'py-3',
    this.small ? 'py-1' : 'py-3',
    this.small ? 'font-light' : 'font-semibold',
    this.small ? 'border-[1px]' : 'border-2'
  ]

  ngOnInit(): void {
    console.log(this.outline)
    this.classes.forEach((val) => {
      this.renderer.addClass(this.el.nativeElement, val);
    })
  }
}

HTML

<button air-btn [outline]="true">Continue with Google</button>

Any solution appreciated!

You should initialize the classes array inside ngOnInit.

import { Directive, ElementRef, Input, OnInit, Renderer2 } from '@angular/core';

@Directive({
  selector: '[air-btn]'
})
export class AirBtnDirective implements OnInit {
  @Input() small?: boolean;
  @Input() outline?: boolean;

  constructor(private el: ElementRef, private renderer: Renderer2) {}

  classes: string[] = [];

  ngOnInit(): void {
    this.classes = [
      'relative',
      'disabled:opacity-70',
      'disabled:cursor-not-allowed',
      'rounded-lg',
      'hover:opacity-80',
      'transition',
      'w-full',
      this.outline ? 'bg-white' : 'bg-rose-500',
      this.outline ? 'border-black' : 'border-rose-500',
      this.outline ? 'text-black' : 'text-white',
      this.small ? 'text-sm' : 'text-md',
      this.small ? 'py-1' : 'py-3',
      this.small ? 'py-1' : 'py-3',
      this.small ? 'font-light' : 'font-semibold',
      this.small ? 'border-[1px]' : 'border-2',
    ];
    console.log(this.outline);
    this.classes.forEach((val) => {
      this.renderer.addClass(this.el.nativeElement, val);
    });
  }
}