JavaScript Interview Questions (Coding based questions)
The article provides solutions to several JavaScript programming challenges, including functions for reversing words, calculating factorials, capitalizing the last letter of words, removing duplicate characters, flattening arrays, and working with recursive exponentiation. It also covers understanding JavaScript concepts such as hoisting, closures, scope, object properties, and asynchronous behavior. Various code snippets are presented to illustrate these concepts, highlighting common pitfalls and expected outputs in different scenarios.
Q. Reverse each word in the sentence.
Solution:
const reverseEachWord = (str) => {
let words = str.split(' ');
words = words.map(word => word.split('').reverse().join(''));
return words.join(' ');
}
Q. Write a recursive function for calculating the factorial of a number.
Solution:
const factorial = (num) => {
if(num === 1) {
return num * 1;
}
return num * factorial(num - 1);
}
Q. Write a function to capitalize the last letter from a sentence.
Solution:
const capitalizeLastLetterFromSentence = (str) => {
let words = str.split(' ');
words = words.map(word => {
const len = word.length -1;
word = word.slice( 0, word.length -1) + word[word.length -1].toUpperCase();
return word;
});
return words.join(' ');
}
Q. Write a function to remove duplicate characters from a sentence.
Solution:
const removeDuplicates = (str) =>[...new Set(str.split(''))].join('')
Q. Write a function to flatten a given array.
Solution:
const flattenArray = inputArray => {
const output = [];
while (inputArray.length) {
let value = inputArray.shift();
if (Array.isArray(value)) {
inputArray = value.concat(inputArray);
}
else {
output.push(value);
}
}
return output;
}
Q. Write a function to return reverse of a string.
Solution:
const reverseStr = (str) => [...str].reverse().join('');
Q. Write a function to calculate the smallest number in given of digits.
e.g. 125 => In 3 digits smallest number is 100
5454 => In 4 digits smallest number is 1000
9 => smallest number is 1.
Solution:
const calculateSmallestNumber = (num) => {
const length = String(num).match(/\d/g).length;
return Math.pow(10, length - 1);
}
Q. Write a function to group the elements based on a given key.
Solution:
const groupBy = (input, key) => {
const output = {};
input.forEach( item => {
if(output[item[key]] === undefined) {
output[item[key]] = [];
}
output[item[key]].push(item);
});
return output;
}
Q. Write a function to compute the exponent of a number use recursion.
Solution:
const exponent = (a, n) => {
if (n === 0) {
return 1;
}
else {
return a * exponent(a, n - 1);
}
};
Q. Write the output of the below code snippets.
(Outputs not added)
Code:
var x = 21;
var girl = function () {
console.log(x);
var x = 20;
};
girl ();
Code:
(function(params) {
console.log(1);
setTimeout(() => {
console.log(2);
}, 1000);
setTimeout(() => {
console.log(3);
}, 0);
console.log(4);
})();
Code:
var foo = function bar(){
return 7;
}
console.log(typeof bar);
Code:
var a = {};
var b = a;
a.v = 1;
b.v = 2;
console.log(a.v)
Code:
q = 1;
(function(){
q = 2;
if(true){
let q = 3;
}
function f1(){
var q = 4;
}
f1();
console.log('inside: ', q)
})();
console.log('q: ', q)
Code:
(function(){
var q = 1;
if(true){
var q = 3;
}
function f1(){
var q = 2;
}
f1();
console.log('q: ', q)
})();
Code:
q = 1;
(function(){
q = 2;
if(true){
var q = 3;
}
function f1(){
q = 4;
}
f1();
})();
console.log('q: ', q)
Code:
let a = [1, 2, 3];
a.x = 'foo';
let b = '';
for (i of a) {
b += i;
}
console.log(b); //123
Code:
const x = {
m: 42,
f: function(){
let a = [1, 2, 3];
let str = "";
a.forEach(function(){
str += this.m;
});
return str;
}
}
console.log(x.f());
Code:
for (var i = 0; i < 5; i++) {
setTimeout(function () { console.log(i); }, i * 1000);
// prints 5 after 5 times each after a second
}
Code:
var z = 1, y = z = typeof y;
console.log(y); //undefined
console.log(undefined === undefined);
console.log(null === null);
console.log(NaN === NaN);
const x = 2 + 5 + +"3"
console.log(x, typeof x);
Code:
var strA = "hi there";
var strB = strA;
strB = "bye there!";
console.log(strA);
console.log(NaN === NaN);
Code:
function add(num1, num2) {
return
num1 + num2;
}
Code:
for (let q = 0; q < 5; q++) {
setTimeout(() => {
console.log('Using let and timeout: ', q * 1000);
}, q * 1000);
// prints 0, 1000, 2000, 3000, 4000 after every sec
}
Code:
for (let q = 0; q < 5; q++) {
setTimeout(() => {
console.log('Using let: ', q);
}, 1000);
//prints 0, 1, 2, 3, 4, 5 after 1 sec
}
Code:
for (var q = 0; q < 5; q++) {
setTimeout(() => {
console.log('Using var and timeout: ', q * 1000);
}, q * 1000);
// prints 5000 after each sec
}
Code:
for (var q = 0; q < 5; q++) {
setTimeout(() => {
console.log('Using var: ', q);
}, 1000);
//prints 5 after a sec
}
Code:
function Teacher(name, age) {
this.name = name;
this.age = age;
}
function Person(name, age) {
Teacher.call(this, name, age);
this.name = 'person';
}
const data = new Person('name', 25);
console.log(data);
delete data.name;
console.log(data);
Code:
const obj = {
x: 'test',
a: function () {
const x = 'value';
console.log('a -- > ', this.x, x);
},
b: function hello() {
function test() {
const x = 'hello';
console.log('b -- > ', this.x, x);
}
test();
},
c: () => {
const x = 'temp';
console.log('c -- > ', this.x, x);
},
d(){
const x = 'temp';
console.log('d -- > ', this.x, x);
}
}
obj.a();
obj.b();
obj.c();
obj.d();
Code:
class Xyz {
constructor(){
this.m = 100
}
test1(){
setTimeout((function () {
console.log(this.m)
}).bind(this), 0);
}
test2(){
setTimeout((function () {
console.log(this.m)
}), 0);
}
test3(){
setTimeout(function () {
console.log(this.m)
}, 0);
}
test4(){
setTimeout(() => {
console.log(this.m)
}, 0);
}
}
new Xyz().test1();
new Xyz().test2();
new Xyz().test3();
new Xyz().test4();
Code:
class Xyz {
constructor(){
this.m = 100
}
test1(){
setTimeout((function () {
console.log(this.m)
}).bind(this), 0);
}
test2(){
setTimeout((function () {
console.log(this.m)
}), 0);
}
test3(){
setTimeout(function () {
console.log(this.m)
}, 0);
}
test4(){
setTimeout(() => {
console.log(this.m)
}, 0);
}
}
new Xyz().test1();
new Xyz().test2();
new Xyz().test3();
new Xyz().test4();
Code:
function promised(msg) {
return new Promise((resolve) => {
setTimeout(function () {
resolve(msg);
}, 3000);
});
}
const async_fn = async function () {
const p1 = await promised('first_first');
console.log(p1);
const p2 = await promised('seconds_first');
console.log(p2);
console.log('done_first');
};
async_fn();
Code:
function promised(msg) {
return new Promise((resolve) => {
setTimeout(function () {
resolve(msg);
}, 3000);
});
}
const p1 = promised('first');
p1.then((res) => console.log(res));
const p2 = promised('seconds');
p2.then((res) => console.log(res));
console.log('done');