We have two simple methods — one method in Java one method in C#. Both of these two methods get one parameter and return parameter+1 after it. I changed this sample for testing an object input not primitive value.

C# (Part I)    

Java (Part I)

JavaScript (Part I)

Also, you can see our parameter does not change after call function sum.

We change param type from integer to a class with a one property as integer.

C# (Part II)

Java (Part II)

JavaScript (Part II)

Now we change the code and create new instance in sum method of input object:

C# (Part III)

Java (Part III)

Now I change call by value to reference:

C# (Part IV)

Java (Part IV)

So we have an error here. You simply can’t do that in Java, since Java doesn’t support pointers …

But in JavaScript:

1. JavaScript is always pass by value, but when a variable refers to an object (including arrays), the “value” is a reference to the object.
2. Changing the value of a variable never changes the underlying primitive or object, it just points the variable to a new primitive or object.
3. However, changing a property of an object referenced by a variable does change the underlying object.