JavaScript fundamentals: Variables and Data types

A variable is a container in which we assign a value to for storage.

Rules of naming variables

Starts with a lowercase letter.

Has no spaces and uses camelCasing eg myLuckyNumber

Does not use reserved words.

Datatypes

a) Primitive data types

111.1
1
"This is a string"
`This is also a string`
'This is another string'
""

Numbers, Strings, Booleans, Undefined, Symbol, Null

b)Structured

Objects, Functions

Numbers: JavaScript provides a numeric data type for working with numerical values, including integers and floating-point numbers. For example:

let quantity = 10;
let price = 19.99;
let total = quantity * price;
console.log("Total: $" + total.toFixed(2));

In this example, we declare variables to store quantity and price. We then perform a calculation to determine the total cost by multiplying the two variables. The toFixed() method ensures that the total is displayed with two decimal places.

Strings: Strings are used to represent textual data. They are enclosed within single quotes (‘’) or double quotes (“”) in JavaScript. For example:

let message = "Hello, World!";
let name = "John";
console.log(message + " My name is " + name + ".");

In this example, we declare a message variable with a greeting and a name variable with a person’s name. We then concatenate these variables and output the combined message using the + operator.

Booleans: Booleans are either true or false. They are used for logical operations, conditional statements, and decision-making. For example:

let isLogged = true;
let isAdmin = false;
if (isLogged) {
  console.log("User is logged in.");
}
if (!isAdmin) {
  console.log("User is not an admin.");
}

In this example, we declare variables to represent whether a user is logged in (isLogged) and whether they have admin privileges (isAdmin). We use conditional statements (if) to check the boolean values and output corresponding messages based on the conditions.

Undefined: When a variable is declared but not assigned a value, it is undefined. For example:

let firstName;
console.log(firstName); // Output: undefined

In this example, we declare a variable firstName but don't assign any value to it. When we output the variable, it returns undefined since it doesn't have a defined value.

Null: Null represents the intentional absence of any object value. For example:

let userDetails = null;
console.log(userDetails); // Output: null

In this example, we assign the value null to the variable userDetails, indicating that there is no user information available.

Symbol: Symbols are unique and immutable data types introduced in ECMAScript 6. For example:

const id = Symbol("id");
const user = {
  [id]: "abc123",
  name: "John Doe",
};
console.log(user[id]); // Output: abc123

In this example, we create a symbol id and use it as a key in an object. Symbols are often used as unique identifiers to avoid naming conflicts.