The this Keyword

this refers to "the object the current method was called on" — but unlike Python's explicit self, JavaScript sets it automatically based on how a function is called, which is a common source of bugs.

class Counter {
    count = 0;

    increment() {
        this.count++;
    }
}

const counter = new Counter();
const fn = counter.increment;
// fn(); // would throw — "this" is lost when detached like this

const arrowFn = () => counter.increment();
arrowFn(); // works — arrow functions don't have their own "this"

Common mistakes

• Passing a class method as a callback directly (e.g. to button.addEventListener("click", obj.method)) and losing its this — wrap it in an arrow function instead: () => obj.method().