What Is Reference Type Data Type?


Larry Thompson

In JavaScript, there are two main data types: reference type and primitive type. In this article, we will focus on understanding the reference type data type and how it differs from the primitive type.

What is a Reference Type Data Type?

A reference type data type refers to objects in JavaScript. Unlike primitive types, which include numbers, strings, booleans, null, and undefined, reference types are more complex and can hold multiple values.

Reference types are created using constructor functions or object literals. Some examples of reference types in JavaScript include:

  • Arrays: Arrays in JavaScript are objects that can hold multiple values of different data types. They are created using square brackets [] and can be accessed by their index.
  • Objects: Objects are collections of key-value pairs.

    They can store various data types as property values and are created using curly braces {}.

  • Functions: Functions in JavaScript are also reference types. They can be assigned to variables, passed as arguments to other functions, or used as return values.

The Difference Between Reference Types and Primitive Types

The key difference between reference types and primitive types is how they are stored and accessed in memory.

Primitive types, such as numbers or booleans, are stored directly in memory when assigned to a variable. When you assign a new value to a variable that already holds a primitive value, the original value is replaced with the new one.

Reference types, on the other hand, store a reference to their value in memory rather than the actual value itself. This means that when you assign a reference type to a variable or pass it as an argument to a function, you are actually working with a reference to the original value. As a result, changing the value of a reference type variable will also change the original value it references.

Working with Reference Types

When working with reference types, it’s important to keep in mind how they are stored and accessed in memory. Here are some key considerations:

  • Equality: When comparing two reference type values using the equality operator (== or ===), JavaScript checks if they refer to the same location in memory rather than comparing their values.
  • Passing by Reference: When passing a reference type as an argument to a function, any changes made to the object within the function will affect the original object outside of the function as well.
  • Copying Values: If you want to create a copy of a reference type object without affecting the original, you need to perform a deep copy rather than simply assigning it to another variable.

Example: Working with Arrays

To illustrate how reference types work, let’s consider an example using arrays:

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


console.log(arr1); // Output: [1, 2, 3, 4]
console.log(arr2); // Output: [1, 2, 3, 4]

In this example, both `arr1` and `arr2` refer to the same array in memory. Therefore, when we push a new value into `arr2`, it also affects `arr1` because they both point to the same array object.


Understanding reference type data types is crucial for working with objects, arrays, and functions in JavaScript. Unlike primitive types, reference types store a reference to their value rather than the actual value itself. This has implications on how they are stored, accessed, and manipulated in memory.

By grasping the concept of reference types and their behavior, you’ll be better equipped to write JavaScript code that effectively works with complex data structures.

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