index.md

title	tags	order	date	answers
Pass by Value	object mutability data types	24	2019-10-02	football, "Lisa prefers Johnny", Chris R roofsitting, "Lisa prefers Mark", Doggy roofsitting, "Lisa prefers Johnny", Doggy // correct football, "Lisa prefers Mark", Chris R

When setting variables equal to each other and then changing one of them, does it change the other? Consider the following code. What is logged?

let a1 = {
  name: 'Johnny',
  hobby: 'football'
};

let b1 = 'Lisa prefers Johnny';

let c1 = ['Denny', 'Michelle', 'Chris R'];

let a2 = a1;
let b2 = b1;
let c2 = c1;

a2.hobby = 'roofsitting';
b2 = 'Lisa prefers Mark';
c2[2] = 'Doggy';

console.log(a1.hobby);
console.log(b1);
console.log(c1[2]);

Because a2 and c2 refer to the same objects in memory as a1 and c1, when their properties hobby and [2] were changed, those changes could also be seen through a1 and c1. The change made to b2 was not changing a property, rather, replacing the b2 variable itself. Replacing a variable with a new value has no effect on the original value, so b1 remained unchanged.