Reference

Objects are never copied. They are passed around by reference. An object's reference is a value that refers to an object. When you create an object using the new operator or object literal syntax, JavaScript creates an object and assigns a reference to it.

Here's an example of creating an object using the object literal syntax:

var object = {
  foo: 'bar'
};

Here's an example of creating an object using the new operator:

var object = new Object();
object.foo = 'bar';

When you assign an object reference to a variable, the variable simply holds a reference to the object, not the object itself. This means that if you assign the object reference to another variable, both variables will point to the same object.

For example:

var object1 = {
  foo: 'bar'
};

var object2 = object1;

console.log(object1 === object2); // Output: true

In the example above, both object1 and object2 are variables that hold references to the same object. The === operator is used to compare the references, not the objects themselves, and it returns true because both variables hold references to the same object.

Following is an example of creating an object by reference.

// Imagine I had a pizza
let myPizza = { slices: 5 };
// And I shared it with You
let yourPizza = myPizza;
// I eat another slice
myPizza.slices = myPizza.slices - 1;
let numberOfSlicesLeft = yourPizza.slices;
// Now We have 4 slices because myPizza and yourPizza
// reference to the same pizza object.
let a = {},
  b = {},
  c = {};
// a, b, and c each refer to a
// different empty object
a = b = c = {};
// a, b, and c all refer to
// the same empty object