Primitive value vs Reference value

Question

I read a book called \"Professional Javascript for web developer\" and it says: \"Variable is assigned by Reference value or Primitive Value. Reference values are objects st

Answer 1

Primitive versus reference:

Variable are segments of memory (RAM) which the javascript engine reserves to hold your data. Within these variables can be stored 2 kinds of values:

• Actual data: For example a string or number. This means that the actual memory (i.e. the bytes in memory) hold the data itself.
• References to objects: For example Array objects or Function objects. This means that this variable just holds a reference to another location in memory where this object resides.

Difference between primitive and reference value:

When a primitive value gets assigned to a variable the data (values of the bits) just copied. For example:

Primitive values:

let num1 = 10;

// What happens here is that the bits which are stored in the memory container 
// (i.e. variable num1) are literally copied into memory container num2
let num2 = num1;

Reference values:

let objRef1 = {prop1: 1}

// we are storing the reference of the object which is stored in objRef1
// into objRef2. Now they are pointing to the same object
let objRef2 = objRef1;

// We are manipulating the object prop1 property via the refernce which
// is stored in the variable objRef2
objRef2.prop1 = 2;

// The object which objRef1 was pointing to was mutated in the previous action
console.log(objRef1);