100+ JavaScript Coding Interview Questions, from ScriptVerse.DEV

Here are 100+ short interview questions in JavaScript!

Q1. Reverse the string:

Welcome to the Jungle

It should read:

Jungle the to Welcome

Answer/Solution

              
                let str = "Welcome to the Jungle";

                console.log(str.split(" ").reverse().join(" "));

Q2. Reverse the string:

Welcome to the Jungle

in the format:

elgnuJ eht ot emocleW

Answer/Solution

              
                let str = "Welcome to the Jungle";

                console.log(str.split("").reverse().join(""));

Q3. Given a string

Welcome to the Jungle

reverse each word in the sentence:

emocleW ot eht elgnuJ

Answer/Solution

              
                let str = "Welcome to the Jungle";

                const revStr = (str, separator) => {
                  return str.split(separator).reverse().join(separator);
                };

                let t = revStr(str, "");

                console.log(revStr(t, " "));

Q4. How do you check if a given object is an array?

Answer/Solution

              
                let a = [];

                console.log(Array.isArray(a));

Q5. How do you empty an array?

Answer/Solution

              
                let a = [1, 2, 3];
                a.length = 0;

                // or a.splice(0, a.length);
                console.log(a);

Q6. Duplicate the array `a = [1,2,3]`

Answer/Solution

              
                let a = [1, 2, 3];

                console.log(a.concat(a));

                // [1,2,3,1,2,3]

Q7. Write a function to check the equality of two arrays

Answer/Solution

              
                const areEqual = (a, b) => {
                  return Array.isArray(a) && Array.isArray(b)
                    && (a.length === b.length)
                    && (a.every((itm, idx) => itm === b[idx]));
                };

Q8. Write a function called `mul()` which returns the product of three numbers and is invoked as `mul(3)(4)(5)`

Answer/Solution

              
                const mul = (a) => (b) => (c) => a * b * c;

                console.log(mul(1)(2)(3));

Q9. Write a function to check if two strings are an anagram

Answer/Solution

              
                let word = "peach";
                let anotherWord = "cheap";

                const isAnagram = (f, s) => {
                  let a = f.toLowerCase();
                  let b = s.toLowerCase();

                  a = a.split("").sort().join("");
                  b = b.split("").sort().join("");

                  return a.localeCompare(b) === 0 ? true : false;
                };

                console.log(isAnagram(word, anotherWord));

Q10. Swap the values of the two strings

a = "Carpe" and b = "Diem"

Answer/Solution

              
                let a = "Carpe";
                let b = "Diem";

                [a, b] = [b, a];

                console.log(a);
                console.log(b);

Q11. How do you remove all the falsy values from the array?

Answer/Solution

              
                let arr = [1, undefined, null, false, null, 6, 9];

                console.log(arr.filter(Boolean));

Q12. How do you remove all the repetitive elements from an array?

Answer/Solution

              
                let arr = [1, 1, 1, 2, 7];

                console.log([...new Set(arr)]);

Q13. How do you convert an array into an object?

Answer/Solution

              
                let birds = ['Sparrow', 'Magpie', 'Crane'];

                console.log({ ...birds });

Q14. How do you convert an object into an array?

Answer/Solution

              
                const man = {
                  name: 'John Doe',
                  gender: 'Male'
                };

                console.log(Object.values(man));

Q15. How do you convert a string into an array?

Answer/Solution

              
                let language = 'English';

                console.log(language.split(''));

Q16. How do you flatten an array?

Answer/Solution

              
                let arr = [1, [2, 3], [4, 5], 6];

                arr.flat();

                // or

                [].concat(...arr);

Q17. How do you test if an object is empty?

Answer/Solution

              
                Object.entries(obj).length === 0

Q18. Given the string: `"this is a string"`, find the number of "i", "s" and "t" occurring in the string.

Answer/Solution

              
                let a = "this is a string";

                function countLetters(str, letter) {
                  const re = RegExp(letter, 'g');
                  const count = str.match(re).length;
                  return count;
                }

                console.log(countLetters(a, 'i')); // 3
                console.log(countLetters(a, 's')); // 3
                console.log(countLetters(a, 't')); // 2

Q19. Test if the first character of a string is CAPITALIZED or not?!

Answer/Solution

              
                let re = /^[A-Z]/;
                let str = "Lakme";

                console.log(re.test(str));

Q20. Test if all characters in a string are LOWERCASED or not?!

Answer/Solution

              
                function isLower(s) {
                  var pattern = /^[a-z]+$/;
                  return pattern.test(s);
                }

Q21. What is the Regex for the number format `XXX-XXXXXXXX` or `XXXXXXXXXXX`?

Answer/Solution

              
                /\d{3}-?\d{8}/g

Q22. Select all words starting with the letter `p`.

Answer/Solution

              
                /\b p /g

Q23. Write a regex that accepts only numbers.

Answer/Solution

              
                /^\d+$/g

              
                /^[0-9]+$/

Q24. Write a regex that accepts only characters.

Answer/Solution

              
                /^\[A-Za-z]+$/g

Q25. Write a regex that accepts a 10-digit phone number.

Answer/Solution

              
                /^\d{10}$/g

Q26. What will be the output of the following?

            
              if (false) {
                var a = 1;
                let b = 2;
              }

              console.log(a); // undefined
              console.log(b); // Reference Error

Answer/Solution

undefined and Reference Error

Q27. What will be the output of the following?

            
              let id = Symbol("id'");
              console.log(typeof id);

Answer/Solution

symbol

Q28. What will be the output of the following?

            
              (function () {
                var a = b = 1;
              })();

              console.log(a); // Reference Error
              console.log(b); // 1

Answer/Solution

Reference Error and 1

Q29. What will be the output of the following?

            
            this.n = 2; // 'this' refers to global window object
            var number = {
              n: 3,
              getN: function () { return this.n; }
            };

            console.log(number.getN()); // 3

            
              this.n = 2; // 'this' refers to global window object
              var number = {
                n: 3,
                getN: () => { return this.n; }
              };

              console.log(number.getN()); // 2

Answer/Solution

3 and 2

Q30. What is the difference between Object.freeze() and Object.seal()?

Answer/Solution

Object.freeze() prevents any changes to existing properties and prevents adding or removing properties. Object.seal() prevents adding or removing properties, but existing writable properties can still be changed.
Q31. What is the difference between .match() and .matchAll() in Regular Expressions?

Answer/Solution

.match() returns the occurrence as strings, and .matchAll() returns an iterator of all matches as arrays.

Q32. What is the output of

            
              console.log(typeof typeof 1);

Answer/Solution

string

Q33. What is the output of

            
              console.log(0.1 + 0.2 == 0.3);

Answer/Solution

false

Q34. How do you check if a number is an Integer?

            
              let n = 1;
              console.log(Number.isInteger(n));

Answer/Solution

true

Q35. What will be the result of the following?

            
              let n = 1.0;
              console.log(Number.isInteger(n));

Answer/Solution

true

Q36. A function is defined as

function f() {}

What will be its Boolean output? What is typeof f?

            
              function f() {};
              console.log(f ? 1 : 2); // 1
              console.log(typeof f); // function

Answer/Solution

true

Q37. What will be the result of the program?

            
              var y = 1;

              if (function f() {}) {
                y += typeof f;
              }

              console.log(y); // 1undefined

Answer/Solution

1undefined

← PREV JavaScript Interview Questions

100+ JavaScript Coding Interview Questions, from ScriptVerse.DEV

Q1. Reverse the string:

Q2. Reverse the string:

Q3. Given a string

Q4. How do you check if a given object is an array?

Q5. How do you empty an array?

Q6. Duplicate the array `a = [1,2,3]`

Q7. Write a function to check the equality of two arrays

Q8. Write a function called `mul()` which returns the product of three numbers and is invoked as `mul(3)(4)(5)`

Q9. Write a function to check if two strings are an anagram

Q10. Swap the values of the two strings

Q11. How do you remove all the falsy values from the array?

Q12. How do you remove all the repetitive elements from an array?

Q13. How do you convert an array into an object?

Q14. How do you convert an object into an array?

Q15. How do you convert a string into an array?

Q16. How do you flatten an array?

Q17. How do you test if an object is empty?

Q18. Given the string: `"this is a string"`, find the number of "i", "s" and "t" occurring in the string.

Q19. Test if the first character of a string is CAPITALIZED or not?!

Q20. Test if all characters in a string are LOWERCASED or not?!

Q21. What is the Regex for the number format `XXX-XXXXXXXX` or `XXXXXXXXXXX`?

Q22. Select all words starting with the letter `p`.

Q23. Write a regex that accepts only numbers.

Q24. Write a regex that accepts only characters.

Q25. Write a regex that accepts a 10-digit phone number.

Q26. What will be the output of the following?

Q27. What will be the output of the following?

Q28. What will be the output of the following?

Q29. What will be the output of the following?

Q30. What is the difference between `Object.freeze()` and `Object.seal()`?

Q31. What is the difference between `.match()` and `.matchAll()` in Regular Expressions?

Q32. What is the output of

Q33. What is the output of

Q34. How do you check if a number is an Integer?

Q35. What will be the result of the following?

Q36. A function is defined as

Q37. What will be the result of the program?

100+ JavaScript Coding Interview Questions, from ScriptVerse.DEV

Q1. Reverse the string:

Q2. Reverse the string:

Q3. Given a string

Q4. How do you check if a given object is an array?

Q5. How do you empty an array?

Q6. Duplicate the array a = [1,2,3]

Q7. Write a function to check the equality of two arrays

Q8. Write a function called mul() which returns the product of three numbers and is invoked as mul(3)(4)(5)

Q9. Write a function to check if two strings are an anagram

Q10. Swap the values of the two strings

Q11. How do you remove all the falsy values from the array?

Q12. How do you remove all the repetitive elements from an array?

Q13. How do you convert an array into an object?

Q14. How do you convert an object into an array?

Q15. How do you convert a string into an array?

Q16. How do you flatten an array?

Q17. How do you test if an object is empty?

Q18. Given the string: "this is a string", find the number of "i", "s" and "t" occurring in the string.

Q19. Test if the first character of a string is CAPITALIZED or not?!

Q20. Test if all characters in a string are LOWERCASED or not?!

Q21. What is the Regex for the number format XXX-XXXXXXXX or XXXXXXXXXXX?

Q22. Select all words starting with the letter p.

Q23. Write a regex that accepts only numbers.

Q24. Write a regex that accepts only characters.

Q25. Write a regex that accepts a 10-digit phone number.

Q26. What will be the output of the following?

Q27. What will be the output of the following?

Q28. What will be the output of the following?

Q29. What will be the output of the following?

Q30. What is the difference between Object.freeze() and Object.seal()?

Q31. What is the difference between .match() and .matchAll() in Regular Expressions?

Q32. What is the output of

Q33. What is the output of

Q34. How do you check if a number is an Integer?

Q35. What will be the result of the following?

Q36. A function is defined as

Q37. What will be the result of the program?

Q6. Duplicate the array `a = [1,2,3]`

Q8. Write a function called `mul()` which returns the product of three numbers and is invoked as `mul(3)(4)(5)`

Q18. Given the string: `"this is a string"`, find the number of "i", "s" and "t" occurring in the string.

Q21. What is the Regex for the number format `XXX-XXXXXXXX` or `XXXXXXXXXXX`?

Q22. Select all words starting with the letter `p`.

Q30. What is the difference between `Object.freeze()` and `Object.seal()`?

Q31. What is the difference between `.match()` and `.matchAll()` in Regular Expressions?