Everything About JavaScript Data Types

In JavaScript, data types define the kind of value that can be stored and manipulated. JavaScript is a dynamically typed language, meaning variables can hold values of any data type, and the type can change at runtime.

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JavaScript Data Types

JavaScript has two main categories of data types:

1. Primitive Types

2. Reference Types

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1. Primitive Types

These are immutable (cannot be changed) and directly represent a single value.

Primitive Data Types:

1. Number:

   • Represents both integers and floating-point numbers.

   • Example:

       let age = 25;
       let price = 19.99;
     

2. BigInt:

   • Used to represent integers larger than Number.MAX_SAFE_INTEGER (2^53 - 1).

   • Example:

       let largeNumber = 1234567890123456789012345678901234567890n;
     

3. String:

   • Represents text, enclosed in single ('), double ("), or backticks (` ).

   • Example:

       let name = 'John';
       let greeting = `Hello, ${name}`;
     

4. Boolean:

   • Represents true or false.

   • Example:

       let isLoggedIn = true;
     

5. Undefined:

   • A variable that has been declared but not assigned a value.

   • Example:

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

6. Null:

   • Represents an intentional absence of any value.

   • Example:

       let data = null;
     

7. Symbol:

   • Represents a unique, immutable value, often used as property keys.

   • Example:

       let id = Symbol('uniqueId');
     

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2. Reference Types (Objects)

These are mutable and can store collections of values or more complex entities.

Reference Data Types:

1. Object:

   • A collection of key-value pairs.

   • Example:

       let user = { name: 'Alice', age: 30 };
     

2. Array:

   • An ordered list of values.

   • Example:

       let colors = ['red', 'green', 'blue'];
     

3. Function:

   • A block of reusable code.

   • Example:

       function greet() {
         console.log('Hello!');
       }
     

4. Date:

   • Represents dates and times.

   • Example:

       let today = new Date();
     

5. RegExp:

   • Represents regular expressions for pattern matching.

   • Example:

       let pattern = /abc/;
     

6. Map, Set, WeakMap, WeakSet:

   • Special objects for key-value storage (Map) or unique values (Set).

   • Example:

       let map = new Map();
       let set = new Set();
     

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Special Considerations

Dynamic Typing:

A variable's type can change at runtime:

let value = 42;        // Number
value = 'Hello';       // String
value = true;          // Boolean

Type Checking:

Use typeof to check the type of a value:

console.log(typeof 42);          // "number"
console.log(typeof 'Hello');     // "string"
console.log(typeof true);        // "boolean"
console.log(typeof null);        // "object" (a known quirk in JavaScript)
console.log(typeof undefined);   // "undefined"

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Primitive vs. Reference Types

Example:

// Primitive
let a = 10;
let b = a;
b = 20;
console.log(a); // 10 (a is not affected)

// Reference
let obj1 = { name: 'Alice' };
let obj2 = obj1;
obj2.name = 'Bob';
console.log(obj1.name); // "Bob" (obj1 is affected)

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Summary

• JavaScript has 7 primitive types: Number, BigInt, String, Boolean, Undefined, Null, and Symbol.

• All other types are reference types, primarily Object and its variations (e.g., Array, Function).

• Use typeof to check types and understand whether a value is primitive or reference.