What are JavaScript Objects, Properties, and Methods?

In JavaScript, objects are used to store multiple values. Commonly, an object contains properties and methods. Objects are the same as variables. Usually, the variable stores a single value while the object stores multiple values.

Definition of Property and Method

Properties are the key value-based pair that should have a colon in the between. Following is an example,

const student = {
    firstName: "James",
    lastName: "Robert",
    age: 12,
    admissionFee : 200,
    monthlyFee : 50 
};

This student object has five properties which are strings and integers.

Methods are the same as JavaScript’s usual function in which any action can be done. It attaches to the property.

Let’s suppose we need to sum up the admission and monthly fee we can do it in the object by adding a method.

const student = {
    firstName: "James",
    lastName: "Robert",
    age: 12,
    admissionFee : 200,
    monthlyfee : 50,
    totalFee : function() {
    return this.admissionFee + this.monthlyfee;
    } 
};

In this example, totalFee property has a method that sums the admission and monthly fee. If you notice in the object’s method, we have this keyword. In JavaScript, when we use this inside object, it refers to the object. In above example admissionFee is accessed through this keyword. So this.admissionFee returns admissionFee property of student object. Let’s call the method into the browser console and see the result.

console.log(student.totalFee());
// Output: 250

Objects can be stored to constant and variable with both var and let keywords. Following are the examples,

  • const student = {}; // object stored into student constant
  • var student = {}; // object stored into student variable with var key
  • let student = {}; // object stored into student variable with let key

Access Object Property and Method

Object property can be accessed through a dot property accessor and square brackets. Following is an example of a dot property accessor

object.property

Similarly, object property can be accessed through square brackets, both ways return the same result.

object[property]

Let’s access the first and last names of the student object.

console.log(student.firstName);
// Output: James

console.log(student.lastName);
// Output: Robert

We can also access the property through square brackets, the same as we access array items. Below is an example,

console.log(student['firstName']);
// Output: James

We can access the object method through the dot property accessor.

object.property + parentheses ()

Let’s access the totalFee property to get the total fee,

console.log(student.totalFee());
// Output: 250