simple concept of javascript

simple-concept-of-js.js

/*
* 1. MUTABLE VS IMMUTABLE 
*/
// CASE 1
let a = 1;
let b = a;
console.log(b);  // No.1
b = 3;
console.log(a); // No.2
console.log(b)  // No.3
/*
* Result:
* No.1: 1
* No.2: 1
* No.3: 3 
*/

// CASE 2
let orderA = { total: 3_000 };
let orderB = orderA;
console.log(orderB);  // No.1
orderB = { total: 5_000 };
console.log(orderA); // No.2
console.log(orderB)  // No.3
/*
* Result:
* No.1: 3000
* No.2: 3000
* No.3: 5000
*/

// CASE 3
const order = {total: 30_000};
order.total = 50_0000;
console.log(order.total);
// Result: 50_000

// CASE 4
const orderO = {total: 30_000};
const orderP = orderO;
console.log(orderP); // No.1
orderP.total = 50_000;
console.log(orderO); // No.2  
console.log(orderP); // No.3
/*
* Result:
* No.1: 30000
* No.2: 50000
* No.3: 50000
*/

/**
* CLOUSURE
*/
for (var i = 0; i < 3; i++) {
    const log = () => {
      console.log(i); 
    };

    setTimeout(log, 100);
}
//Result: 3, 3, 3

for (let i = 0; i < 3; i++) {
    const log = () => {
      console.log(i); 
    };

    setTimeout(log, 100);
}
// result: 1, 2, 3