JavaScript Value vs. Reference Types

In JavaScript, data types are broadly classified into two categories:  

1. Primitive (Value) Types:

   • Store the actual value directly.  
      
   • Examples:
     • Number (e.g., 10, 3.14)
     • String (e.g., “hello”, ‘world’)
     • Boolean (e.g., true, false)
     • null (represents the intentional absence of a value)
     • undefined (represents a variable that has been declared but has no value assigned)
     • Symbol (unique and immutable values)

2. Reference Types:

   • Store a reference (memory address) to the actual value.  
      
   • Examples:
     • Object (e.g., { name: "John", age: 30 })
     • Array (e.g., [1, 2, 3])
     • Function

Key Differences:

• Assignment:

  • Value Types: When assigned to a new variable, a new copy of the value is created. Changes to the new variable do not affect the original.
  • Reference Types: When assigned to a new variable, both variables point to the same memory location. Changes made to one variable will also affect the other.  
     

     

• Example:

  JavaScript

   

  // Value Type (Number)
  let num1 = 10;
  let num2 = num1; 
  num2 = 20; 
  console.log(num1); // Output: 10
  
  // Reference Type (Array)
  let arr1 = [1, 2, 3];
  let arr2 = arr1; 
  arr2.push(4); 
  console.log(arr1); // Output: [1, 2, 3, 4] 
  

Understanding this distinction is crucial for writing correct and predictable JavaScript code, especially when dealing with object manipulation and function arguments.