JavaScript Primitive vs. Reference Values

Summary: in this tutorial, you will learn the differences between primitive and reference values.

Accessing by value and reference

In JavaScript, a variable may store two types of values: primitive and reference.

JavaScript provides six primitive types as undefined, null, boolean, number, string, and symbol , and a reference type object.

The size of a primitive value is fixed, therefore, JavaScript stores the primitive value on the stack.

On the other hand, the size of a reference value is dynamic so JavaScript stores the reference value on the heap.

When you assign a value to a variable, the JavaScript engine will determine whether the value is a primitive or reference value.

If the value is a primitive value, when you access the variable, you manipulate the actual value stored in that variable. In other words, the variable that stores a primitive value is accessed by value.

Unlike a primitive value, when you manipulate an object, you work on the reference of that object, rather than the actual object. It means a variable that stores an object is accessed by reference.

To determine the type of a primitive value you use the typeof operator. For example: