20 JavaScript Array Methods Interview Questions and Answers

Array methods are a fundamental part of JavaScript, and as such, are often used in web development interviews to test a candidate’s knowledge of the language. While there are many different array methods, some are more commonly used than others. In this article, we will review some of the most commonly used array methods and how you can use them to answer interview questions.

JavaScript Array Methods Interview Questions and Answers

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

1. What is an Array in JavaScript?

An Array in JavaScript is a data type that is used to store a collection of data. Arrays can be used to store any type of data, including numbers, strings, and objects. Arrays are often used to store data that is related, such as a list of items or a set of instructions.

2. Can you explain the difference between a list and an array in JavaScript?

A list is an ordered collection of items, while an array is a specialized type of list that can be used to store data in a structured way. In JavaScript, arrays are used to store data in a way that is similar to how they are used in other programming languages.

3. How do you create an array in JavaScript?

There are a few ways to create an array in JavaScript. The most common way is to use the array constructor, which looks like this:

var myArray = new Array();

You can also create an array by using the array literal syntax, which looks like this:

var myArray = [];

Both of these methods will create an empty array. You can then add elements to the array by using the push() method.

4. How do you add a new item to an array in JavaScript?

There are a few ways to add a new item to an array in JavaScript. The most common way is to use the push() method, which will add the new item to the end of the array. You can also use the unshift() method, which will add the new item to the beginning of the array.

5. How can you access items in an array using their index position?

There are a few ways to access items in an array using their index position. The first is to use the square bracket notation, which looks like this:

array[index]

You can also use the .length property to loop through an array and access each item:

for (var i = 0; i < array.length; i++) {
console.log(array[i]);
}

6. How can you remove the first element of an array in JavaScript?

There are a few ways to do this, but one of the most common is to use the shift() method. This method will remove the first element from an array and return it.

7. Can you give me some examples of real-world uses for arrays?

There are many real-world uses for arrays. Some examples include:

– storing a list of items (such as a to-do list)
– storing a list of user-inputted data
– storing a list of files or folders in a directory
– storing a list of search results

8. How do you sort the elements of an array in ascending order by default in Javascript?

The sort() method in Javascript will sort the elements of an array in ascending order by default.

9. Is it possible to reverse the order of elements stored in an array in JavaScript? If yes, then how would you go about doing that?

Yes, it is possible to reverse the order of elements stored in an array in JavaScript. The easiest way to do this would be to use the built-in reverse() method. This method will reverse the order of the elements in the array, and then return the reversed array.

10. What is the best way to find duplicate values from an array in JavaScript?

The best way to find duplicate values from an array in JavaScript is to use the filter() method. This method will return a new array with only the duplicate values from the original array.

11. Why does JavaScript not support multi-dimensional arrays?

The main reason why JavaScript does not support multi-dimensional arrays is because the language is designed to be lightweight and easy to use. Adding support for multi-dimensional arrays would make the language more complicated and would add to the overall size of the code.

12. What are sparse arrays in JavaScript?

A sparse array is an array that has been created with a large number of elements, but with only a few of those elements actually having values assigned to them. The rest of the elements are simply empty, or “sparse.” This can be useful in certain situations where you need to create an array with a lot of elements but only need to assign values to a small number of them.

13. What are several ways to loop through an array in JavaScript?

There are several ways to loop through an array in JavaScript. The most common way is to use a for loop, which you can use to iterate through the array index by index. Another way to loop through an array is to use the forEach() method, which allows you to execute a callback function on each element in the array. You can also use the map() method to create a new array based on the results of the callback function.

14. What is the maximum size of an array in JavaScript?

There is no maximum size for an array in JavaScript.

15. What’s the difference between null and undefined?

Null is a value that represents no value, while undefined is a value that represents a value that has not yet been defined. In other words, null is an empty value, while undefined is a value that has not yet been assigned a meaning.

16. What happens when you try to print an array with more than one dimension?

When you try to print an array with more than one dimension, the output will be a comma-separated list of the array’s elements.

17. What is the function used to sort the elements of an array in descending order in JavaScript?

The function used to sort the elements of an array in descending order in JavaScript is the sort() function. This function takes an optional parameter which is a function that defines the sort order.

18. How can you define an associative array in JavaScript?

An associative array is a type of array that uses strings as its keys instead of numbers. This allows you to store data in a more organized way, and it also makes it easier to retrieve specific data when you need it. To create an associative array in JavaScript, you simply need to create a new object and use string keys instead of numbers.

19. Can you explain what an object is in JavaScript?

In JavaScript, an object is a data type that is composed of a collection of unordered properties. Objects are used to store data in a structured format.

20. What is the difference between var, let, and const declarations?

The main difference between var, let, and const is that var is function-scoped, let is block-scoped, and const is block-scoped and immutable. This means that variables declared with var can be accessed anywhere within the function they are declared in, while variables declared with let can only be accessed within the block they are declared in. Const declarations are also immutable, meaning that the value of the variable cannot be changed once it is declared.