Variables and Datatypes in JavaScript

JavaScript is dynamically typed, meaning variables don’t have fixed types. Variables store values, and JavaScript has different data types to classify them.

JavaScript provides three ways to declare variables:

• var – Function-scoped, can be redeclared (not recommended).

• let – Block-scoped, can be reassigned.

• const – Block-scoped, cannot be reassigned.

•         var x = 10; // Old way
          let y = 20; // Preferred for reassignments
          const z = 30; // Cannot change
  

  JavaScript Data Types

  Two main categories:

  1. Primitive Types (stored by value):

     • String → "Hello"

     • Number → 42, 3.14, NaN

     • Boolean → true, false

     • BigInt → For very large numbers

     • Symbol → Unique identifiers

     • Undefined → No assigned value

     • Null → Intentional absence of value

📌 Example:

    let name = "John"; // String
    let age = 25; // Number
    let isStudent = true; // Boolean

2. Non-Primitive (Reference) Types (stored by reference):

   • Object → { name: "Alice", age: 30 }

   • Array → [1, 2, 3]

   • Function → () => "Hello!"

📌 Example:

    let person = { name: "Alice", age: 30 }; // Object
    let numbers = [1, 2, 3, 4]; // Array

Type Checking

• JavaScript allows us to check the type of the datatype that we are using by using the following command and the returned value will be the datatype that we are using.

• Use typeof to check types:

    console.log(typeof "Hello"); // "string"
    console.log(typeof 42); // "number"
    console.log(typeof null); // "object" (quirk)

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Conclusion

• Prefer let and const over var as it may cause some confusion.

• Use typeof to check data types.