Javascript Interview Questions and Answers

JavaScript is an important language in the world of web development and programming. It is used to create interactive effects within web browsers, allowing users to take more control over their browsing experience. If you’re preparing for a job interview that involves JavaScript, it’s important to know the basics of the language and be familiar with some of the more common interview questions. Here are some of the most commonly asked JavaScript interview questions and answers.

Following are the famous Javascript Interview Questions and Answers:

What is the difference between let, var, and const in JavaScript?

In JavaScript, the three keywords let, var, and const are used to declare variables. The difference between these three keywords is the type of scope they provide. var is used to declare a global or function-scoped variable, while let and const are used to declare block-scoped variables. let also allows the reassignment of values, while const does not.

When working with variables, it’s important to consider which type of scope is best for the situation. For instance, if you want a variable to remain constant, const is the best option. If you need to reassign values, however, let should be used instead.

What is the use of the prototype in JavaScript?

A prototype is an object that is used to add methods and properties to an existing object. It is an important concept in JavaScript as it enables us to extend the functionality of existing objects. For example, if we have a Person object, we can add a walk method to it by using the prototype.

The prototype is also used in inheritance. By using the prototype, it is possible to create a new object which contains all the methods and properties from the original object, as well as any new methods and properties that we have added.

What are closures in JavaScript and how are they used?

Closures are functions that are defined inside other functions and have access to the variables of their parent functions. They are used to create private data or to create functions that can be reused in different contexts. For example, a closure can be used to create a function with access to a variable that is not in the global scope.

Closures are also used to create functions that can be called with different arguments, but still, have access to the original data. This is often used when creating reusable functions that can be used in different contexts.

What are the differences between Java and JavaScript?

Java and JavaScript are two different programming languages, but there are some similarities between them. Both languages are used for web development and are based on the ECMA-262 standard.

Java is a more traditional language and is compiled at runtime. JavaScript, on the other hand, is a scripting language and is interpreted at runtime. In addition, Java has a more complex syntax and is object-oriented, while JavaScript is a scripting language and is not object-oriented.

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

The double equals (==) operator is used to compare two values and returns true if they are equal. It does not consider the type of values. On the other hand, the triple equals (===) operator is used to compare two values and returns true only if they are equal and of the same type.

For example, 5 == '5' returns true, while 5 === '5' returns false.

How do you create a for loop in JavaScript?

A for the loop is used to execute a set of statements repeatedly until a certain condition is met. It is composed of three parts: the initializer, the condition, and the updater. The initializer is used to set the starting value for the loop, the condition determines when the loop should end, and the updater changes the value of the initializer.

For example, a for a loop that iterates from 0 to 10 can be written as follows:

for (let i = 0; i < 10; i++) {
// Statements

What is the difference between an array and an object in JavaScript?

An array is a special type of object that is used to store multiple values in a single variable. Each value is accessed using an index. Arrays are also ordered and can contain any type of data.

An object, on the other hand, is a collection of key-value pairs. Each value is accessed using a key, which is usually a string. Unlike arrays, objects are usually unordered and can contain any type of data.

How do you debug a JavaScript application?

Debugging a JavaScript application involves examining the code for errors and finding the cause of any unexpected behaviour. There are various tools available for debugging JavaScript applications, such as the Chrome DevTools and the Firefox Developer Tools. These tools allow you to set breakpoints, view the call stack, and examine variables.

What is a callback in JavaScript?

A callback is a function that is passed as an argument to another function. When the callback is called, it is executed with the context of the function it was passed to. Callbacks are used to execute code after an asynchronous operation is completed or to call a function repeatedly at a given interval.

What is the use of an asynchronous function in JavaScript?

An asynchronous function is used to execute code outside of the main execution thread. This is useful for long-running operations that do not need to be executed in the main thread. For example, making an API call or sending an AJAX request can be done asynchronously so that the main thread does not have to wait for the request to be completed.

Hope this blog helped you to get Javascript Interview Questions and Answers. Thanks for reading!!


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