JavaScript

Question 1

get ASCII code of a letter

Answer 1

“abcd”.charCodeAt(0)

Question 2

get letter from ASCII code

Answer 2

String.fromCharCode(97)

Question 3

string to array

Answer 3

str.split(“”) or str.split(“,”) or str.split(/[|,]/g)

Question 4

match a string in a sentence

Answer 4

let text = “The rain in SPAIN stays mainly in the plain”;
let matchArray = text.match(/ain/gi);

Question 5

Check if a string includes “world”

Answer 5

text.includes(“world”);

Question 6

to return a decimal after a specified precision (rounded off)

Answer 6

let x = 9.656;
x.toFixed(0);
x.toFixed(2);
x.toFixed(4);

Question 7

Check if the value is an integer

Answer 7

Number.isInteger(x)

Question 8

sorting an integer array

Answer 8

array.sort() // asending
array.sort().reverse() // descending
array.sort( (a, b) => b - a )

Question 9

sorting a string array

Answer 9

array.sort() // asending
array.sort().reverse() // descending
array.sort( (a,b) => b.localeCompare(a) ) ) // descending

Question 10

convert array into string ?

Answer 10

array.join(“”)

Question 11

concatenating 2 arrays

Answer 11

const mergedArray = array1.concat(array2);

Question 12

splice() to Remove Elements from Array

Answer 12

const fruits = [“Banana”, “Orange”, “Apple”, “Mango”]; fruits.splice(0, 1); // [“Orange”, “Apple”, “Mango”];

Question 13

take a slice of array

Answer 13

const fruits = [“Banana”, “Orange”, “Lemon”, “Apple”, “Mango”]; const citrus = fruits.slice(1, 3); // [“Orange”, “Lemon”]

Question 14

Create an array from a string

Answer 14

let array = Array.from(“ABCDEFG”)

it has same effect as let array = “ABCDEFG”.split(“”)

Question 15

Print all values of an array

Answer 15

for(let x of array) {
console.log(x)
}

// prints the values. “of” is for values

Question 16

Print the indexes of an array

Answer 16

for(let x in array) {
console.log(x)
}

// prints indexes. “in” is for indexes

Question 17

Remove duplicates from an Array

Answer 17

let array = [1,2,3,3,4,1,2,5,6,7,8,8]
let set = new Set(array);

Question 18

Iterating a Set

Answer 18

for( let x of set.values() ) {
   console.log(x)
}
	
	

Question 19

Iterating a Map

Answer 19

for( let x of map.keys() ) {
  console.log(fruits.get(x))
}

Question 20

Define a class in JS

Answer 20

class Car {
constructor(name, year) {
this.name = name;
this.year = year; }
age() {
const date = new Date(); return date.getFullYear() - this.year;
}
}

Question 21

RegEx for a whitespace character

Answer 21

/\b/

Question 22

RegEx for alphanumeric character

Answer 22

/\w/
This includes [A-Za-z0-9_]
if we want to extend this to special characters, we need to add
[\w@#$]

Question 22

RegEx for alphanumeric character

Answer 22

/\w/
This includes [A-Za-z0-9_]
if we want to extend this to special characters, we need to add
[\w@#$]