JavaScript Object References and Copying

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Non-primitive data types like objects can be stored and copied by reference.

See the examples below:

Primitive data type

const name = 'Bello';
const myName = name;

console.log(myName); // Bello

Non-primitive data type

const obj = { name: 'Bello', favNum: 9 }; 
const person = obj; // copy the reference

console.log(person); // { name: 'Bello', favNum: 9 }
console.log(person.favNum); // 9

The object { name: 'Bello', favNum: 9 } is assigned to the variable obj to store its address in memory. Think of obj like a sheet of paper with an address in it. That is, person copied the reference to the object obj.

Accessing the value of the object (person.favNum) looks for the address of obj through person

The object obj itself is not duplicated

We can also modify the object content.

const obj = { name: 'Bello', favNum: 9 }; 
const person= obj; // copy the reference

console.log(person); // { name: 'Bello', favNum: 9 }

person.favNum = 69;

console.log(person); // { name: 'Bello', favNum: 69 }

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Comparison by reference

Two objects are equal only if they are the same object.

const a = {};
const b = a; // copy the reference

console.log(a == b); // true, both variables reference the same object
console.log(a === b); // true

Since a and b reference the same object, thus they are equal.

Here also two independent objects are not equal, even though they look alike (both are empty):

const a = {};
const b = {}; // two independent objects

console.log(a == b); // false

Happy coding!

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