Quick JavaScript Go through for Revision Purposes.

Talk is Cheap, Show me the Code - Linus Torvalds

Introduction

What are Variables?

• Variables store information in a JavaScript program.
• They act like labeled boxes to hold data.

Creating Variables

• Use let to create a variable.
• Example: let message;

Assigning Values

• Put data into a variable using =.
• Example: let message = 'Hello';

Accessing Data

• Retrieve data from a variable using its name.
• Example:

let message = 'Hello';
alert(message); // Shows the variable content


Declaring Multiple Variables

• Declare multiple variables on separate lines for better readability.
• Example: let user = 'John'; let age = 25; let message = 'Hello';

Variable Naming Rules

• Variable names contain letters, digits, $, and _.
• The first character can't be a digit.
• Use camelCase for multiple words.
• Examples: let userName; let test123;

Constants

• Declare constants using const.
• Constants cannot be changed after assignment.
• Example:

const myBirthday = '18.04.1982';


Uppercase Constants

• Use uppercase and underscores for constants with known values.

• Example:

const COLOR_RED = "#F00";


Variable Naming Best Practices

• Choose clear and meaningful variable names.
• Avoid short or cryptic names.
• Make your code self-explanatory.
• Example:

let currentUser;
let shoppingCart;


Avoid Reusing Variables

• Create new variables instead of reusing existing ones.
• Clear, separate variables lead to better code quality.

JavaScript Data Types

1. String

• Used for text data.
• Enclosed in single (''), double ("") quotes, or backticks (``).
• Example:

const name = 'John';


2. Number

• Represents whole numbers or decimals.
• Example:

const age = 25;
const price = 19.99;


3. BigInt

• For very large numbers, append 'n' to the end.
• Example:

const bigIntValue = 900719925124740999n;


4. Boolean

• Represents true or false values.
• Used for logical decisions.
• Example:

const isRaining = true;


5. undefined

• Represents uninitialized variables.
• Example:

let lastName;


6. null

• Represents an empty or unknown value.
• Example:

const emptyValue = null;


7. Symbol

• Unique and immutable data type.
• Introduced in newer JavaScript versions (ES2015+).
• Example:

const uniqueSymbol = Symbol('description');


8. Object

• Used to store collections of data.
• Consists of key-value pairs.
• Example:

const person = { name: 'Alice', age: 30 };


JavaScript Type

• JavaScript determines data types automatically.
• A variable can change its type during execution.

JavaScript typeof

• Use typeof operator to check the type of a variable.
• Example:

typeof(name); // returns "string"
typeof(age); // returns "number"
typeof(isRaining); // returns "boolean"
typeof(uniqueSymbol); // returns "symbol"


Use it as a quick Go through in case of Revision, etc.
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