20 JavaScript Puzzles Interview Questions and Answers

If you want to work with JavaScript, you need to be prepared to answer some tough questions during your interview. Many employers will give you a puzzle to test your problem-solving skills and see how you think on your feet. While there is no one right way to solve a puzzle, there are some strategies you can use to improve your chances of success. In this article, we will share some tips on how to approach JavaScript puzzles during your interview.

JavaScript Puzzles Interview Questions and Answers

Here are 20 commonly asked JavaScript Puzzles interview questions and answers to prepare you for your interview:

1. Write a function to return the nth element of an array.

function getNthElement(arr, n) {
if (n < 0 || n >= arr.length) {
return undefined;
}
return arr[n];
}

2. How would you check if a number is an integer?

There are a few different ways to check if a number is an integer in JavaScript. One way would be to use the Number.isInteger() method, which returns true if the number is an integer and false otherwise. Another way would be to use the Math.floor() method, which rounds a number down to the nearest integer. If the number you are checking is already an integer, then it will not be changed by this method.

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

The == operator will compare the values of two variables, but will not take into account the type of data that is stored in each variable. The === operator, on the other hand, will compare both the value and the type of data in each variable, meaning that two variables with different types but the same value will not be considered equal.

4. Can you explain what NaN means in JavaScript?

NaN stands for “Not a Number,” and it indicates that a value is not a valid number. This can happen when trying to perform mathematical operations on values that are not numbers, such as strings or null values.

5. Can you describe how event bubbling works in JavaScript?

Event bubbling is a feature of JavaScript that allows events to propagate up through the DOM tree. When an event is triggered on an element, it will first be handled by that element, and then by its parent, and then by its parent’s parent, and so on. This can be useful if you want to have a single event handler that can be used for multiple elements, but it can also be confusing if you’re not expecting it.

6. Is it possible to assign multiple classes to an HTML element using JavaScript? If yes, then how can you do that?

Yes, it is possible to assign multiple classes to an HTML element using JavaScript. You can do this by using the element’s className property. For example:

“`
element.className = “class1 class2 class3”;
“`

7. How do you convert a numeric value into a string in JavaScript?

There are a few ways to convert a numeric value into a string in JavaScript. One way is to use the toString() method, which is a built-in method that is available on all JavaScript objects. Another way is to use the String() constructor, which will also return a string representation of the numeric value.

8. Can you give me some examples of primitive and non-primitive data types in JavaScript?

Primitive data types in JavaScript include Boolean, null, undefined, number, and string. Non-primitive data types include objects, arrays, and functions.

9. Can you create an instance of a String object in JavaScript?

Yes, you can create an instance of a String object in JavaScript. The following code creates a String object and assigns it to the variable myString:

var myString = new String(“this is a string”);

10. Can you explain how prototypal inheritance works in JavaScript?

Prototypal inheritance is a bit different than classical inheritance, but it is still a very important part of JavaScript. In classical inheritance, objects are created by using a class as a template. In prototypal inheritance, objects are created by using another object as a template. The object that is used as a template is called a prototype.

When an object is created using a prototype, the new object will have all of the same properties and methods as the prototype. This is different than classical inheritance, where an object will only have the properties and methods that are defined in the class.

One of the benefits of prototypal inheritance is that it is much easier to create objects that inherit from other objects. This is because all you need is a prototype object, and you don’t need to define a whole class.

11. Can you explain what typeof does in JavaScript?

typeof is an operator that returns a string containing the type of the operand. The operand can be of any type.

12. Can you explain what arrays are in JavaScript?

Arrays are a type of data structure that allows you to store a collection of data in a single variable. In JavaScript, arrays are created using the array constructor, which takes in a list of values and returns an array object. You can access individual elements of an array using their index, and you can add or remove elements from an array using the push and pop methods.

13. What’s the best way to merge two or more arrays in JavaScript?

The best way to merge two or more arrays in JavaScript is to use the Array.concat() method. This method returns a new array that is the result of concatenating the given arrays.

14. Do all browsers support ECMAScript 5?

No, not all browsers support ECMAScript 5.

15. What’s the output of the following code: var x = 3 + 2 + ‘1’;

The output of the code is ’61’. This is because JavaScript automatically converts numbers to strings when they are concatenated with strings. Therefore, the 3 and 2 are converted to ‘3’ and ‘2’, and then ‘1’ is concatenated onto the end, resulting in ’61’.

16. What will be the output of this code snippet? console.log(typeof typeof 1);

The output of this code snippet will be “string”. This is because the typeof operator returns a string value that represents the data type of the operand. In this case, the operand is the number 1, which has a data type of “number”. Therefore, the typeof operator will return the string “number”.

17. What will the following code print out? console.log(1 < 2 < 3); console.log(3 > 2 > 1);

The first code will print out “true” and the second code will print out “false”.

18. What is currying?

Currying is a technique in functional programming whereby a function is called with fewer arguments than it is expecting, and returns a new function that takes the remaining arguments. This can be useful for creating new functions from existing ones that have some arguments already filled in.

19. What tool should I use for unit testing my JavaScript code?

There are a few different options available for unit testing JavaScript code, but one of the most popular is Jest. Jest is a JavaScript testing framework that is designed to be easy to use and to provide a good testing experience. It can be used to test React applications, and it has a wide range of features that make it a good choice for unit testing.

20. What are static properties and methods?

Static properties and methods are those that are associated with a class, but not with any particular instance of that class. A static method can be called without creating an instance of the class, and a static property can be accessed without an instance as well.