How does this keyword in JavaScript work?

The JavaScript this keyword refers to the object it belongs to. It has different values depending on where it is used. In a method, this refers to the owner object. Alone, this refers to the global object. In a function, this refers to the global object. In a function, in strict mode, this is undefined. In an event, this refers to the element that received the event. Methods like call(), and apply() can refer to this to any object.

let dog = {
  name: "Spot",
  numLegs: 4,
  sayLegs: function() {return "This dog has " + this.numLegs + " legs.";}
};

console.log(dog.sayLegs());
// Outputs "This dog has 4 legs."

Reference:

https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/object-oriented-programming/make-code-more-reusable-with-the-this-keyword

https://www.w3schools.com/js/js_this.asp