Mordern JavaScript

JavaScript.js

hola

Output

In the following code, I expected both a and b to be 3. However, a is undefined and b is 3. Why?

(function(){
var a = b = 3;
})();

console.log(typeof a);//"undefined"
console.log(b);//3

---

---

Actually it is

var a = 3;
b = 3

b = 3 is an assignment without a declaration. Since there is no b in the current execution context (the IIFE), JavaScript engine looks for b in the outer lexical environment. In this case, the outer environment is the global execution context.
Since b is not found in the global execution context either, and assuming non-strict mode, JavaScript implicitly creates b as a property of the global object (e.g., window.b in browsers). This makes b a global variable.

Destructuring

Prototype

class Hola{
    constructor(){
        this.name="yogendra";
        console.log(this);
    }

    static div(){
        console.log("div");
    }

    sum(){
        console.log("sum");
    }
}

const h = new Hola();

console.log(Object.getPrototypeOf(h))   // {constructor: ƒ, sum: ƒ}

console.log(h.__proto__)   // {constructor: ƒ, sum: ƒ}

console.log(Hola.prototype); // {constructor: ƒ, sum: ƒ}

Array.at()

Get the value at that position -> index passed
const arr = ["jack","yogi","abc"]
console.log(arr.at(0)) // "jack"
console.log(arr.at(-1)) // "abc"

This keyword

Akshay -> https://www.youtube.com/watch?v=9T4z98JcHR0&list=PLlasXeu85E9eWOpw9jxHOQyGMRiBZ60aX&index=9