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0.2 Primitive & Complex Data Types

Every piece of information in JavaScript has a Data Type. Understanding types and how JavaScript automatically converts them is essential to writing bug-free code.

1. The 7 Primitive Data Types

Primitives are basic, single values stored directly in memory:

Number: Integers and decimals (e.g. 42, 3.14, -10)
String: Text enclosed in quotes (e.g. "Hello", 'JS', `Template`)
Boolean: Logical truth values (true or false)
Undefined: A variable declared but assigned no value yet
Null: Intentional empty value (explicitly empty)
BigInt: Super large integers beyond standard Number range
Symbol: Unique, immutable identifier

2. Complex Types: Objects & Arrays

Unlike primitives, complex data structures can store multiple values grouped together:

                    // Object: Key-Value pairs 

                    let person = { name: "Alex", age: 25 }; 
 
                    // Array: Ordered list of values 

                    let colors = ["Red", "Green", "Blue"];

3. Type Coercion (Implicit vs Explicit)

JavaScript is dynamically typed. Variables can hold any type, and JS often auto-converts types (Implicit Coercion):

"10" + 5 → "105" (Plus operator concatenates strings!)
"10" - 5 → 5 (Minus operator forces numeric conversion!)
Explicit Conversion: Number("10"), String(42), Boolean(1)

📌 KEY POINTS TO REMEMBER

`null` vs `undefined`: undefined means "uninitialized by system", whereas null means "deliberately cleared by programmer".
Historical JS Bug: typeof null returns "object" due to an early 1995 implementation quirk in JavaScript.
`typeof` operator: Use typeof myVar to check any variable's data type at runtime.

⚡ Interactive Visual: Coercion & Type Explorer

Test how JS evaluates implicit coercion and check `typeof` outputs:

Click any test button above.