55 #javascript interview questions

1.

 const myString = 'Hello 2020'; 
 myString = 'Hello World!';
 console.log(myString)//"Hello World!"

what block scope keyword when changed produces the above console.log output?

2

 let students = 0;
 let classroom = false;
 if(students > 10) {
    let classroom = true;
   }
console.log(classroom);

What is console-.log'd? (false or true)

3

let num1 = [1,2,3,4];
let num2 = [10,20,30,1];
let num3 = [100,200,300,1]; 

Find the common elements in all 3 arrays

4

function checkout(price,___){
  if(price > 100){
   ___( ____ );
  }
}

function _____( ____){
  let discount = ____ - (.10 *_____);
   console.log("the total is" + discount)
}
checkout(110,cb);

5

const yummies = ['Ice-cream','Cupcake','Donut','Cupcake'];

Using filter( ), return the unique elements from "yummies"

6

Code a function that returns a promise

7

const composers = [{
 Name: 'Beethoven',
 Genre: 'Classical',
 Rating: '9'
},
{
 Name: 'Mozart',
 Genre: 'Classical',
 Rating: '10'
 }]

Use map () to create a new array of objects with the rating & last name

8

let c = 0;
let d = false;
console.log(c !== d);

9

let catPowers ={ 
 snarky: true,
 napzinger: "Zzzzz",
 gobbler: function(){
  if(this.snarky === true)
    return this.snarky;
  }
}

return only the values of the catPowers object without using for-in

10

let numArray1 =[1,2,3];
let numArray2= numArray1;
numArray2.push(4);

Take a guess what will console.log(numArray1) be?

11

What #ES6 method will you use to create a shallow-copied array of characters from this string referenced by let myString?

let myString = ? ("supercalifragilisticexpialidocious");

12

let obj1 = { a: 10, b:20, c:30 }; 
let obj2 = { d: 40, e:50, f:60}; 
let obj3 = { g: 70, h:80, i:90 }; 
let obj;

Assign all properties from obj1,obj2, obj3 to obj

13

let devFood = [ "Foo Bar", "Barzinga","Loodles"];
console.log(devFood)//["Foo Bar", "Foo Bar", "Barzinga"];

Use an #ES6 method to copy array elements to match the console.log

14

var helloWorld = function(msg){
  alert(msg);
}
helloWorld('Hello World');

Re-write this using functional #javascript

15

let games = ["King's Quest", "Super Mario", "Zelda", "Contra"];
games.splice(2, 0, "Doom", "World of Warcraft");
games.slice(0,2);
console.log(games); // ? What will this be

16

what is the difference between the pass by value and pass by reference with examples

17

“innerHTML” can increase the possibility of a XSS attack. What is an alternative for setting text?

18

What is the difference between a 🍬ReferenceError and undefined error 🍡

19

for (var i = 0; i < 10; i++) {
setTimeout(function(){
 console.log(i); //what is logged here?
  }, i * 1000 );
}

20

 let num = 10;  

 function sum( ) {  
  let  num = 100;  
  document.getElementById('myP').innerHTML =(num+num);  // 20 or 200?
   }   

sum( ); 

21

console.log(false != '0')
console.log(false !== '0')

22

let x = null;
/*Knowing that typeof(x) will return “object”. How do you check for a null value?*/

23

let langs = ["JavaScript","C#","Rust","C++","Python"];
  delete langs[3];
  console.log(langs.length);//⭐️
  console.log(langs[3]); //⭐️

24

let arre= ["","A",9,"C++",false];
//Empty the above array  

25

let myQueue = [];
myQueue.push('a');
myQueue.push('b');
myQueue.push('c');
//Remove the first element in myQueue. 💎HINT: FIFO principle

26

console.log(null == undefined) // T or F?
console.log(null === undefined)// T or F?
console.log(typeof(null) === 'object')// T or F?

27

Using in-built methods, implement a stack in #JavaScript and remove the last 2 elements

28

What is event bubbling?🗨️
Is "false" false?🐻
Is " " false?🐻
How do you increase page load times?💻

29

let person1 = {
  name: "Rocko"
};
let person2 = {
  name: "Rover"
};
Object.freeze(person1);http://person1.name  = "Lara"; 
person2 = person1;
console.log(person1);
console.log(person2);

30

let fooBar = new Array(5);
fooBar[2] = "Hello";
console.log(fooBar); //

31

let myArr = [1,10,100,1000,10000]
Array.prototype.first = function() {
return this[0];
}
myArr.pop();
console.log(myArr.first()); // ?💫
console.log(myArr); //? 💫

32

What is a closure? Give an example

33

let x =  y = 7;
y= 10;
console.log(x);
console.log(y); 

34

let game1 = "The Legend of JavaScript"; 
var game2 = "JortNite";
const game3 = "Super Jario";
console.log(window.game1);💎
console.log(window.game2);💎
console.log(window.game3);💎

35

function* generator(num) {
  yield num;
  yield num * 10;
}
let result = generator(100);
console.log(💫);// 100
console.log(💫); //1000

36

function factorial(num) { 
  if (num === 0) {
    return 1;
 } else {
   return num* 🌟(num - 1); //replace the star..
   }        
}
console.log(factorial(4));

37

Write a function to console.log the sum of all the elements in an array using recursion

38

console.log(105 < 232 < 350);
console.log(450 > 333 > 120);  

39

//replicate without 'class':
class coder{  
 constructor(name){  
  http://this.name =name;  
  }  
 detail(){  
   return(http://this.name );
   }  
  }

40

function🐻(i) { 
   let 🔢= function() {
     i++;
    };
    return 🔢; 
}
let 🍎 =  🐻(1000);
let 🍏 = 🐻(1)
🍎(); //?
🍏(); //?

41

let 🍇 = new Set();
🍇.add(1);
🍇.add(5);
🍇.add(1,5)
🍇.add(1, 1000)
console.log(🍇.size); // ⭐️

42

let 🌠 = [
   [35, 28, 29, 31],
   [33, 24, 25, 29]
];
console.log(🌠[0][2]);

A. 35,28
B. 33, 25
C. 29

43

const  🐸= (user, newUser) => {
  return new Promise ((resolve, reject) => {
    if(user === newUser) {
      resolve();
    } else {
      reject();
    }
    })
}

44

/*Re-write this fxn without using an immediately invoked function (with the same functionality):*/

 (function IIFE(){
    console.log( 'hello world!' );
})();

45

const animals  = [“🦊”, “🐸”, “🐹”, “🐰”];
animals.length = 10;
console.log(animals[0]); 
animals.length = 2;
console.log(animals[3]); 

46

//(hint:https://0.30000000000000004.com/ ) :
⭐️console.log(0.1 + 0.2);

47

Write a fxn to reverse a string

48

const codeShop = {
  company: "Code Factory",
  address: "Square building, 10000 Moon St"
}
let 🐧= Object.create(codeShop);
delete🐧.codeShop;
console.log(🐧.company);//⭐️

//❤️hint: hasOwnProperty

49

//⭐️ Duplicate the elements of an array⭐️

function duplicateArr(myArr) {
  return(❓);
}

duplicateArr(["a", "b", "c"]); //["a", "b", "c", "a", "b", "c"]

50

//Complete the following fxn:

function funFxn() {
  let secret = "this is a secret";
❓❓❓❓❓
}

let getSecret = funFxn(); // "this is a secret"

51

//🍎Convert this to an anonymous fxn in #javascript 

function love(param){
  console.log(`I love ${param}`);
}
love("dogs");

52

Define:

1. Event Loop
2. Callback fxn
3. Stack
4. Task queue
5. Higher Order Fxn
6. Var, Const, Let
7. Lexical Scope
8. Closure
9. Anonymous Fxn
10. Event bubbling

53

let arr = [🍓, 🍓, 🍓, 🍓];
arr.❓❓(🥝, 1, 3); 
console.log(arr)//[🍓, 🥝, 🥝,🍓];

54

White space is retained in ES6 template literals? T/F

55

<h2 id="para1"></h2>

localStorage.❓("guestName", "missLorem");
document.getElementById("para1").innerHTML = localStorage.❓("guestName");