Interview Questions-Random Questions

check for undeined/empty/null/false string 

				
					let x = null;
x = undefined;
x = "";
x = 0;
x = Number.NaN;
x = false;

console.log(`%c ${x}`, "color:red;font-size:20px");

if (x) {
  console.log(`%c I have value`, "color:red;font-size:20px");
} else {
  console.log(`%c I am undefined/null/empty`, "color:red;font-size:20px");
}

power of x ^ y

				
					//Short syntax of power of
console.log(2 ** 5); //32

//using Math operation
console.log(Math.pow(2, 5)); //32

use strict

				
					//4.Use Strict
/*
1.cant use a variable without let var or const keyword

2.cant use reserve words as variables
let eval =10 

3.cant delete a variable

4.cant delete a function

Best practice always use - 'use strict'

*/
function useStrict() {
  "use strict";
  result = 10; //this cant be done - rule 1
  let eval = 15; //this cant be done - rule 2
  delete result; //this cant be done - rule 3
  delete useStrict; //this cant be done - rule 4
}

Error?

				
					let @anurag = "anurag";
console.log(@anurag);
//VM3491:1 Uncaught SyntaxError: Invalid or unexpected token

Guess the output

				
					console.log(Number.isNaN(NaN)); //true
//isNaN
//--> checks if its number or not
//-->does type coercion ?? what does it mean ...check below code
console.log(Number.isNaN("2")); //false

Guess the output

				
					//error::->ReferenceError: x is not defined
try {
  console.log(x);
} catch (err) {
  console.error("error::->" + err);
}


//********************************************

try {
  console.log(x);
} catch {
  console.error("error");
}
//it gives you the error 
//catch no need to take parameter..its optional now

Guess the output on IIFE

				
					//IIFE
(function (a, b) {
  console.log((a * b) / b + a);
})(10, 9);

//key points on IIFE
//JS considers above as function expression as it is not starting with function keyword
//func expression means as below
// const x = () =>{} ...
//IIFE is not hoisted by JS engine

10 * 9 =90 
90/9 =10 
10 + 10 =20
Answer - 20

prototypal inheritence

				
					let Study = function (course, level, isAvailableOnPs) {
  this.course = course;
  this.level = level;
  this.isAvailableOnPs = isAvailableOnPs;

  this.courseLevel = function () {
    console.log(this.course + " is for " + this.level);
  };
};

Study.prototype.IsAvailableOnCoursera = function () {
  if (this.isAvailableOnPs) return `${this.course} is available on PluralSight`;
  else return `No ${this.course} is not available on PluralSight!!`;
};

let study1 = new Study("Javascript", "Beginners", true);
let study2 = new Study("Advanced Javascript", "Professionals", false);

study1.courseLevel();
study2.courseLevel();

// Javascript is for Beginners
// Advanced Javascript is for Professionals
// ES new concepts is for Proficient

//Prototypal inheritance..
//Every Object has prototype --> where you can add methods and properties to it
//When you create newly created object using prototype-> the newly created object will
//automatically inherit the properties and methods from already existing parent
//It will try to find out in newly created object first--> if it doesnt find ,,will look for parent object

console.log(study1.IsAvailableOnCoursera());
console.log(study2.IsAvailableOnCoursera());

//Javascript is available on PluralSight
//No Advanced Javascript is not available on PluralSight!!

Primitive/Non-Primitive Data Types

				
					//*******DataTypes**************

typeof 5 --> number
typeof true --> boolean
typeof 'I am string' --> string
typeof undefined --> undefined
typeof null --> object
typeof Symbol('symbol') --> Symbol
typeof {} --> object
console.log(typeof []); //object (Arrays are objects)
typeof NaN --> Number
 
//*******Functions**************

const obj = function () {
  return 5;
};
obj.hello = "hello"; 
 
//Here functions are behaving like objects.you can assign the property
//console.log(obj.hello); // output is hello.

undefined vs null 

				
					//****************************************
console.log(`%c ${undefined === null}`, "color:red;font-size:20px");//false
console.log(`%c ${undefined == null}`, "color:red;font-size:20px"); //true

Memory leak

				
					//********************************
let array= [];
for (let i= 15; i > 1; i++) {
  array.push(i);
}

assign values to variable shortcut

				
					//************Assignment**********************
let a, b, c;
//old way
// a = 1;
// b = 2;
// c = 3;
//new way as below
[a, b, c] = [1, 2, 3];
console.log(`%c ${a} ${b} ${c}`, "color:red;font-size:20px");
//output- 1,2,3

Javascript is a dynamic language

				
					var a = "anurag";
a = 123;
a = true;
console.log(`%c ${a}`, "color:red;font-size:20px");
//output:- true

Leave a Comment