Day 2: Variables and Data Types in JavaScript

Day 2: Variables and Data Types in JavaScript

Welcome to Day 2 of learning JavaScript! Today, we’ll explore the building blocks of any program: variables and data types. These concepts are crucial as they form the foundation for everything you do in JavaScript.

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What Are Variables?

A variable is like a container that holds data values. Think of it as a labeled box where you can store information, retrieve it later, or even change its contents.

Declaring Variables in JavaScript

JavaScript provides three ways to declare variables:

1. var - The old way (avoid using this unless necessary).
2. let - Recommended for variables that can change.
3. const - For variables that shouldn’t change (constants).

Example:

var oldWay = "Avoid this if possible";
let currentWay = "Use let for variables that can change";
const fixedValue = "Use const for constants";

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Difference Between var, let, and const

Feature	var	let	const
Scope	Function-scoped	Block-scoped	Block-scoped
Reassignable	Yes	Yes	No
Redeclarable	Yes	No	No

Example:

function scopeTest() {
    if (true) {
        var x = "Function scope";
        let y = "Block scope";
        const z = "Constant";
    }
    console.log(x); // Accessible
    // console.log(y); // Error: y is not defined
    // console.log(z); // Error: z is not defined
}
scopeTest();

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JavaScript Data Types

JavaScript has two types of data: Primitive and Non-Primitive.

Primitive Data Types

1. String: Textual data. Example:

   let name = "Arjun";
   console.log(name); // "Arjun"

1. Number: Numeric data. Example:

   let age = 22;
   console.log(age); // 22

1. Boolean: True or false values. Example:

   let isStart_up_guy = true;
   console.log(isStart_up_guy); // true

1. Null: Represents an intentional absence of value. Example:

   let emptyValue = null;
   console.log(emptyValue); // null

1. Undefined: A variable that has been declared but not assigned a value. Example:

   let uninitialized;
   console.log(uninitialized); // undefined

1. Symbol: A unique and immutable value. Example:

   let uniqueKey = Symbol("key");
   console.log(uniqueKey); // Symbol(key)

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Type Conversion

JavaScript allows you to convert values between types.

Implicit Conversion (Coercion)

JavaScript sometimes converts types automatically.

Example:

let result = "5" + 5; // String + Number
console.log(result); // "55" (string)

Explicit Conversion

You can manually convert types using built-in functions like Number(), String(), or Boolean().

Example:

let num = "42";
let convertedNum = Number(num);
console.log(convertedNum); // 42 (number)

let boolValue = Boolean(0);
console.log(boolValue); // false

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Practice for Today

1. Declare variables using let and const to store:

   • Your favorite book name.
   • The number of books you own.
   • Whether you like reading.

2. Try type conversion:

   • Convert a number to a string.
   • Convert a string to a number.

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Summary of Day 2

Today, we covered:

1. Variables: var, let, and const.
2. Primitive Data Types: String, Number, Boolean, Null, Undefined, and Symbol.
3. Type Conversion: Implicit and explicit ways to convert types in JavaScript.

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Next Steps

Tomorrow, we’ll dive into operators and expressions in JavaScript to start manipulating data and writing more complex programs. Stay tuned for Day 3: Operators and Expressions!