What are the data types in JavaScript? — JavaScript Interview Question #3

JavaScript is a dynamically-typed language, which means that variables do not have a fixed type at declaration and can change their type during runtime. There are six primitive data types in JavaScript, which include:

Number: This data type is used to represent both integers and floating-point numbers. Numbers can be positive, negative, or zero.

Example:

    var x = 10; // integer
    var y = 3.14; // floating-point number

String: This data type is used to represent textual data. Strings are enclosed in single quotes, double quotes, or backticks.

Example:

    var greeting = 'Hello, world!'; // single quotes
    var message = "It's a beautiful day!"; // double quotes
    var template = `The value of x is ${x}.`; // backticks

Boolean: This data type is used to represent logical values. Boolean values can be either true or false.

Example:

    var isSunny = true;
    var isRaining = false;

Null: This data type is used to represent the intentional absence of any object value. It is often used to indicate that a variable has no value.

Example:

    var myVariable = null;

Undefined: This data type is used to represent a variable that has been declared but has not been assigned a value.

Example:

    var myVariable;
    console.log(myVariable); // Outputs undefined

Symbol: This data type is used to represent unique values that are not equal to any other value. Symbols are often used to create unique identifiers.

Example:

    var id1 = Symbol('id');
    var id2 = Symbol('id');
    console.log(id1 === id2); // Outputs false

In addition to these primitive data types, JavaScript also has two composite data types:

Object: This data type is used to represent a collection of properties. Objects can contain any combination of primitive and composite data types, as well as functions.

Example:

    var person = {
        firstName: 'John',
        lastName: 'Doe',
        age: 30,
        hobbies: ['reading', 'playing music'],
        address: {
            street: '123 Main St.',
            city: 'Anytown',
            state: 'CA'
        },
        sayHello: function() {
            console.log('Hello, my name is ' + this.firstName + ' ' + this.lastName + '.');
        }
    };
    
    console.log(person.firstName); // Outputs 'John'
    console.log(person.hobbies[0]); // Outputs 'reading'
    person.sayHello(); // Outputs 'Hello, my name is John Doe.'

Array: This data type is used to represent a collection of values. Arrays are ordered lists of values, and each value is assigned an index starting from 0.

Example:

    var fruits = ['apple', 'banana', 'orange'];
    console.log(fruits[1]); // Outputs 'banana'

These are the data types available in JavaScript. As a JavaScript expert, I would be happy to provide more information or examples if needed.