JavaScript Objects

An object is a single variable that holds many related values together. Think of a student's admission form: name, course, mobile number, marks — four separate variables, or one object called student that holds all four. An object is like a dabba (a lunch box) with labelled compartments: each compartment has a name (the property) and something inside it (the value).

Diagram — see how it fits together

Objects are everywhere in JavaScript because real life is made of things with details. A chai order has a type, a size, and a price. A cricket player has a name, a team, and a score. Whenever details belong together, an object is the right box for them.

Creating an object

You create an object with curly braces. Inside, you write name: value pairs, separated by commas. This is called an object literal.

let student = {
  name: "Rahul Verma",
  course: "HTML",
  marks: 85
};

Property names are usually written without quotes. Values can be anything — a string, a number, a boolean, an array, or even another object.

Dot vs bracket notation

There are two ways to read a property. Dot notation is the common one: student.name gives "Rahul Verma". Bracket notation does the same with a string: student["name"]. Use the dot when you know the property name while writing the code; use brackets when the property name is stored in a variable, or when it has a space in it.

student.marks = 90;              // change a value with the dot
student["course"] = "CSS";       // change a value with brackets
student.mobile = "9876543210";   // add a brand-new property

You can also add new properties after the object is created, just by assigning them. That is how an admission form grows: first the name, then the course, then the photo.

Methods and this

A property whose value is a function is called a method — it is something the object can do. Inside a method, the word this means "this very object". So this.name inside student means student.name.

let student = {
  name: "Rahul Verma",
  marks: 85,
  pass: function() {
    return this.marks >= 40;
  }
};
student.pass();  // true

Methods keep the data and the actions on it together. The object knows its own marks, and it knows how to check whether it passed.

Common mistakes

• Forgetting the comma between properties — every pair except the last needs a comma after it.
• Writing student.name() when name is a value, not a function — only methods get brackets.
• Using this outside a method — outside an object, this means something else entirely.
• Expecting a copied object to be independent — let b = student copies the reference, not the object.

Remember

• An object groups related values under named properties: { name: "Rahul", marks: 85 }.
• Dot notation (student.name) is the usual way; brackets (student["name"]) work when the name is in a variable.
• A method is a function stored as a property; inside it, this means the object itself.
• An object is a dabba with labelled compartments — dot opens a label, bracket opens any label.

Example explained

• let student = { name: "Rahul Verma", course: "HTML", marks: 85 }; — one object holding three related values, like one admission form.
• pass: function() { return this.marks >= 40; } — a method inside the object. this.marks reads the object's own marks.
• student.marks = 95; — dot notation changes the marks. The button adds 10 bonus marks the same way.
• document.getElementById("info").innerHTML = student.name + ... — builds a line of text from the object's properties and shows it on the page.
• student.pass() — calling the method returns true or false, so the page can say "Passed" or "Failed".