Objects

Key-value pairs

An object groups related data as key: value pairs inside { }. Read a value with dot notation.

<script>
  const user = {
    name: "Asha",
    age: 22,
    city: "Bengaluru",
    isStudent: true
  };
  document.write(user.name + " is " + user.age + " from " + user.city);
</script>

The user object bundles four facts about one person, each as a key: value pair. We then pull values out with dot notation: user.name gives "Asha", user.age gives 22, user.city gives "Bengaluru", and we join them into a sentence.

Read, change, add

<script>
  const car = { brand: "Tata", year: 2024 };
  document.write(car.brand + "<br>");
  car.year = 2025;          // change
  car.color = "blue";       // add new property
  document.write(car.year + " " + car.color);
</script>

First car.brand reads "Tata". Then car.year = 2025 changes an existing property. Then car.color = "blue" adds a brand-new property that was not there before. The final line reads both updated values back out.

These are the everyday operations on an object — reading a value, changing one, and adding one. Here they are as numbered steps:

1. Create the object: const car = { brand: "Tata", year: 2024 } stores two properties to start with.
2. Read a property: car.brand fetches the current value, "Tata".
3. Update a property: car.year = 2025 overwrites the existing year with a new value.
4. Add a property: car.color = "blue" creates a brand-new color key that did not exist before.
5. Read again: car.year and car.color now show the updated and newly added values.

Methods — functions inside objects

A property can also be a function. That is called a method, and inside it the keyword this refers back to the object it belongs to.

<script>
  const person = {
    name: "Ravi",
    greet() { return "Hi, I am " + this.name; }
  };
  document.write(person.greet());
</script>

Calling person.greet() runs the method. Inside it, this.name means "the name of this object", which is "Ravi". So it returns and prints "Hi, I am Ravi".