<input (focus)='functionName()'/>

import { Component } from '@angular/core';
  
@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
  
export class AppComponent {
    onFocus(): void {
        console.log('Focus Is gained for this Element');
    }
}

<br>
<form>
    <input placeholder="Name" (focus) = 'onFocus()'>
</form>

import { Component } from '@angular/core';
  
@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
  
export class AppComponent {
    onFocus(): void {
        console.log('Focus Is gained for this Element');
    }
}

<br>
<form>
    <button (focus) = 'onFocus()'>Click here!</button>
</form>