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Javascript

[JS] What are reference types?

[JS] What are reference types?

Key Learnings of This Post

  • Understand what reference types are in javascript and their characteristics.

What are reference types?

In JavaScript, reference types (also called non-primitive types) are values that are stored in memory by reference, rather than directly containing their value. When you assign or compare a reference type, you are dealing with a reference to the memory location, not the actual value.

✅ JavaScript Reference Types

TypeExampleDescription
Objects ({}){ name: "Alice" }A collection of key-value pairs
Arrays ([])[1, 2, 3]A special type of object used for ordered data
Functions (function)function add(a, b) { return a + b; }A callable object that can be assigned to variables
Dates (Date)new Date()Represents a specific point in time
Regular Expressions (RegExp)/abc/iPattern matching for strings
Maps (Map)new Map()A key-value store that allows any type of key
Sets (Set)new Set()A collection of unique values

Example

const arr1 = [1, 2, 3];
const arr2 = [1, 2, 3];

console.log(arr1 === arr2); // false (Different references)

// you can assign reference
arr3 = arr1;
console.log(arr1 === arr3); // true (Same memory reference)

✅ JavaScript Reference Types v.s. Value Types

TypePrimitive?Stored by Value?Compared by Value?
Number, String, Boolean, null, undefined, Symbol, BigInt✅ Yes✅ Yes✅ Yes
Object, Array, Function, Date, RegExp, Map, Set, etc.❌ No❌ No (Stored by reference)❌ No (Compared by reference)

Summary - characteristics of reference types

✅ Stored in memory by reference

✅ Can be modified even after assignment

✅ Compared by reference, not by value

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