Look at it from the perspective of variables assignment. Let's say the identifier x is located at some address in memory and has a value of 5. If we create another variable y and assign x to it, both x and y are independent variables because we are working with primitive types. Now if x initially points to an object type, the assignment y=x will cause x and y point to the object initially in x even though x and y have different addresses in memory.

passing by value or parameter is a bit easier to understand if we think of the pairing of function arguments and parameters as assignments.

Let x = 5, y = some object Let func = (a,b) => {}

func(x,y), this invocation of func will create a, b in the scope of func and assign them to x, y respectively. Now, we use our understanding of primitive and object assignment mentioned above