this Keyword in Different Contexts

class Component {
  constructor() {
    this.handleClick = this.handleClick.bind(this);
  }
  handleClick() {
    console.log('Clicked');
  }
}

Never, it's optional
Only with event handlers
When methods are used as callbacks
Constructor binding is necessary when: 1) Methods are used as callbacks, 2) Function reference is stored separately, 3) Event handlers need instance context, 4) Alternative to arrow functions, 5) Ensures consistent 'this' binding, 6) Common in class-based components.
Only in React components