Javascript Interview Topics

1. What is the difference between == and === ?

Double equal (==) : converts both the operands to the same type and then compares

Example :

console.log( 2 == ‘2’) ; // true

Triple equal(===) : Does not convert to same type

Example:

Console.log( 2 === 2 ) // false

2. WHAT IS THE VALUE OF 5+6+8+”7"?

The expected output is 197. Since 5,6, and 2 are integers, they will be added numerically. And “7” is a string, its concatenation will be done.

3. What is truthy and falsy values?

Truthy values : There are certain values in Javascript that return true when converted into boolean. Such values are called truthy values.

“false” , “0”, {} (empty object) , & (empty array)

Falsy values: On the other hand there are certain values that return false when coerced to boolean. These values are known as falsy values.

false , 0 , “ ” (empty string) , null, undefined , & NaN

4. Ways to create a variable

There are 3 ways to create a variable in javascript. Var,let and const. Variables created with var are in scope of function (or global if declared in the global scope); let variables are block scoped ; and const variables are like plus their values cannot be reassigned.

Example :

var x = “some value”; //functional or global scopedLet y= “some value”; //block scopedConst z = “some value”; //block scoped + cannot get new value

5. What is Scope?

Scoping is an important topic in JavaScript .Scope in js is an area where you can access or use your declared variables/functions. For private a variable or function or access a variable from all places and how or where to declare it, all discuss this within scoping.

There are two main types of scoping in JavaScript: Global Scope and Local Scope,

6. What is DOM ?

The Document Object Model (DOM) is a programming interface for HTML and XML documents. The Document Object Model (DOM) represents that same document so it can be manipulated. The DOM is an object-oriented representation of the web page, which can be modified with a scripting language such as Javascript.

7. HOW WOULD YOU REVERSE WORDS IN A SENTENCE?

I will check for whitespace and walk through the string. I will also check there multiple white-spaces are present or not. after that, I will reverse the string.

var string = “Welcome to this Blog!”;var reverseEntireSentence = reverseBySeparator(string, “”);// Output becomes !golB siht ot emocleWvar reverseEachWord = reverseBySeparator(reverseEntireSentence, “ “);// Output becomes emocleW ot siht tpircsavaJ !golBfunction reverseBySeparator(string, separator) {return string.split(separator).reverse().join(separator);}

8. Find the largest element in an array javascript

function megaFriend(nameOfFriends) {if (nameOfFriends.length > 0) {var bigName = nameOfFriends[0].length;for (var i = 0; i < nameOfFriends.length; i++) {if (bigName < nameOfFriends[i].length) {var megaName = nameOfFriends[i];}}}else {return ‘this array is empty’;}return megaName;}var nameOfFriends = [‘haris’, ‘tushar’, ‘shakib’, ‘mashrafee’, ‘riad’];bigFriend = megaFriend(nameOfFriends);console.log(bigFriend);//Expected output : mashrafee

9. Generate a random number between 1 to 100 ? The number should be an integer.

const randomNumber = 1 + Math.floor(Math.random() * 100);console.log(randomNumber);

10. Create a Fibonacci Series using a for loop

Fibonacci series is defined as a sequence of numbers in which the first two numbers are 1 and 1, or 0 and 1, depending on the selected beginning point of the sequence, and each subsequent number is the sum of the previous two numbers.

function getFibonacci(n){const fibo = [0,1]for (let i =2; i<=n; i++ ) {fibo [i] = fibo[i -1] + fibo [i -2];}return fibo[n];}console.log ( getFibonacci(9)) //output : 34

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