Top 80+ JavaScript Interview Questions and Answers for 2024 [Updated]
One open-source programming language is JavaScript. It is intended for use in the development of web-based apps. It is substantially faster than other languages because it is interpreted and lightweight. Because JavaScript and HTML are interwoven, using JavaScript in online applications is much simpler.
You can find a thorough list of frequently asked interview questions and responses for JavaScript in this post. It will also assist you in comprehending JavaScript's basic ideas.
To help you prepare for your interviews, we've included a list of frequently asked questions about JavaScript.
JavaScript is a widely used online scripting language that may be used for both server-side and client-side programming. JavaScript code is compatible with object-oriented programming and can be added to HTML pages that web browsers can comprehend and run.
JavaScript is a programming language that is focused on objects.
Java is a computer language that is object-oriented.
Applications written in JavaScript are designed to operate on a web browser.
Applications written in Java are typically designed to run on virtual machines and operating systems.
It is not necessary to compile JavaScript before executing the application code.
Before Java source code can be prepared for real-time execution, it must be compiled.
JavaScript gives otherwise static webpages interaction and allows them to respond to human input.
When using JavaScript, a web page does not need to reload. Take form input validation, for instance.
Web applications' user interfaces (UIs) look and feel significantly better thanks to JavaScript.
Numerous frameworks and libraries for JavaScript are widely used to create web apps and games of all kinds.
JavaScript supports and encourages the use of objects while creating web applications because it is fundamentally an object-oriented programming language.
A variable's scope indicates the locations of its declarations and definitions within a JavaScript program. A variable can have one of two scopes:
In a JavaScript code, global variables with global scope are accessible anywhere.
Local variables can only be accessed from within the function that defines them.
In JavaScript, the object that is now calling is referenced by the this keyword. Constructors frequently utilize it to set values for object properties.
Because functions in JavaScript are objects, they have the ability to accept inputs from other functions and return objects from other functions.
A callback is a JavaScript function that is supplied as a parameter or argument to another function. This function will run anytime the function to which it is provided is run.
The built-in debugger of all contemporary web browsers, including Chrome, Firefox, and others, can be used at any time by pressing the appropriate key, typically the F12 key. The debugging tools provide users with a number of functions.
Additionally, we can debug JavaScript code within a code editor such as Visual Studio Code, Atom, Sublime Text, or any other code editor that we use to develop JavaScript applications.
For your interview preparation, we've included a list of some intermediate level JavaScript interview questions and answers.
A cookie is often a little piece of information that a web browser that was used to view a website sends and stores on the user's computer. Cookies are used to track user behavior on a website and store information for later use.
"key1 = value1; key2 = value2; expires = date" is what document.cookie =;
JavaScript also makes reading a cookie very easy. The document is useful to us.cookies that we just made utilizing that string are contained in the cookie string.
The text.A list of name-value pairs, with the names and values of the cookies separated by semicolons, is stored in the cookie string. Splitting the cookie value into keys and values is another way we may do it with the split() method.
We merely need to provide an expiration date and time in order to erase a cookie. Since certain browsers won't let you delete cookies unless you have a clear path that indicates which cookie to remove from the user's computer, it's a good idea to specify the correct path of the cookie you wish to delete.
"=; Path=/; Expires=Thu, 01 Jan 1970 00:00:01 GMT;"; document.cookie = name + "";
In JavaScript, the terms let and var are used to declare variables and methods. Other than the fact that the let keyword is scoped by a block and the var keyword is scoped by a function, there isn't much of a difference between the two.
Developers and programmers can write JavaScript code more effectively and succinctly by using closures. Every time a variable specified outside of the current scope is accessed within of it, a closure is formed.
log.console(message);
JavaScript functions can be written quickly and succinctly using arrow functions. An arrow function's general syntax is as follows:
"Hello world!" console.log;
This is how a variable is declared, and later on in the JavaScript code, the value can be modified.
This can also be used to define or declare a variable, however unlike variables, their values are fixed for the duration of the JavaScript program and cannot be changed afterwards.
This essentially means that the JavaScript code allows for the values to be modified at a later date.
Writing modular code for our JavaScript apps is made easier by imports and exports. Imports and exports allow us to divide a JavaScript code into several files inside a project. This promotes code readability and significantly reduces the complexity of the application source code.
Calcul.js
Math.sqrt is exported as const sqrt.
Two functions that compute the input's squares and diagonal, respectively, are exported from this file.
main.js
log.console(square(4)); 16
diag(4, 3)); console.log(); // 5
In order to compute square and diagonal, we import those functions and provide input to them.
The document is a property of the Windows object and falls under its purview.
In JavaScript, a window is a global object that stores structure such as functions, variables, locations, histories, and so on.
A multitude of frameworks designed to meet the various needs of the web application development process are included with JavaScript. Among the well-known frameworks are:
Undefined denotes a variable that has been declared but does not yet have a value assigned to it.
variables in a program or application that are not declared or that are not there.
Undefined denotes a variable that has been declared but does not yet have a value assigned to it.
Any variable intended to have no value can have the assignment value null assigned to it.
When a page session expires, the data kept in session storage is either erased or expires.
In order to speed up loading times, websites save certain data locally; this data is retained after a user session ends.
Two forms of data exist in JavaScript: primitive and non-primitive data types.
var y = 5.6; //using a decimal point
Multiple and complex values are stored in non-primitive data types.
give this.x back;
var array1 is equal to [5, "Hello", true, 4.1];
In JavaScript, the keyword this is used to invoke the current object as a constructor and set values for its properties.
Call utilizes each argument in isolation.
return this.name + "Hello";
sayHello.call(obj);
Apply employs an array as a parameter.
return "is" + message + this.name;
applySaySomething(person4, ["awesome"]);
The accessibility of variables and functions at different places in one's code is determined by the scope of variables in JavaScript. A variable can have one of three types of scopes: global, function, or block.
console.log(a*3); // Since a and multiplyBy3 are both written inside the same function, we may access variable "a".
console.log(a); // a throws a reference error since it is written in the local scope and cannot be accessed from outside.
console.log(x); // Since x cannot be accessed outside of the block, it returns a reference error
Since i cannot be accessed outside of the for loop block, console.log(i); // Gives reference error
To write functions with a clear and concise syntax, utilize arrow functions. Furthermore, a function keyword is not needed for declaration. Curly brackets { } allow us to omit an arrow function in a single line of code.
"Hello world!" console.log;
JavaScript's default process behavior, known as "hoisting," involves moving all variable and function declarations to the top of the scope, which can be either local or global.
"Hi There!" console.log(");
even though the variable is declared after it is initialized, console.log(hoistedVariable); // yields 5
In JavaScript, the process of automatically converting a value of one data type into another is known as implicit type coercion.
The code if(a) { console.log(a) } The code will execute within the block since x is equal to 0 (Falsy).
if(b) { log(b) in the console} // The code will execute within the block since y's value is 32 (Truthy).
Indeed, JavaScript is not statically typed; rather, it is dynamically typed.
The Not-a-Number value NaN in JavaScript represents a value that is not a valid number.
In this case, the value assigned by the operator to the number type a=432 is that of a primitive data type. The value of var a returns a new address for var b by allocating a new space in the memory when the var b=a code is executed, causing var b to operate at a new position.
With the aid of a designated operator, the reference to the first variable object, var obj, is transmitted through the location of the second variable, var obj2.
An IIFY, also known as an Immediately Invoked Function, is a function that executes as soon as it is defined. The function must be called in order to be executed; otherwise, the function's declaration is returned.
console.log("Hello world") }; higherOrder(function() {);
Self-invoking functions do not require a request; they are denoted by an automatically invoked function expression followed by (). Nevertheless, the function declaration cannot be called on its own.
Currying is the JavaScript term for the transformation of a function of an argument into functions of one or more arguments.
The many JavaScript object prototypes listed below are used to inherit specific attributes and functions from the Object.prototype.
There are two kinds of faults in JavaScript: logical errors and syntax problems.
Memorization is the term used in JavaScript to describe the process of caching a function's return value with respect to its parameters. It is utilized to expedite the application, particularly when dealing with intricate, time-consuming tasks.
In programming, recursion is a technique used to loop over an action; in contrast, a function calls itself again until the desired result is obtained.
You can create a single object or several objects with comparable attributes and capabilities by using constructor functions.
this.name is equal to name;
this.age is equal to the age;
gender = this.gender;
log.console(person1);
log.console(person2);
With the aid of the charAt() function method, we can extract a character from a specific index.
The Browser Object Model, or BOM, is the interface through which users interact with browsers. A window is the browser's first object. A document, history, screen, navigator, location, and other attributes make up the window object. Nevertheless, there are two ways to call the windows function: directly and by referring the window.
Another name for the prototype design pattern is a property or pattern that is used to create both unique objects and prototypes that are copied from a template with a certain value.
Both a function scope and a global scope exist.
Neither a function scope nor a global scope exist.
Neither a function scope nor a global scope exist.
Block scope is absent.
Block scope is absent.
It is transferable.
It is not transferable.
It is not transferable.
log.console(variable 1);
console.log(differential2);
window.variable1; // Gives 31 as the result
window.variable2; ; gives an undefined result
x.name equals "Radha"; // No exception is raised
In JavaScript, promises can exist in four different states. They are listed in the following order:
A promise is initially in the status of pending. It is the first stage of a promise, when it is neither accepted nor rejected and is in the pending state.
The async action is completed when the promise has been met. This is the stage of fulfillment.
This is the point at which the async action fails and the promise is rejected.
It is the situation in which the promise is accepted or kept.
sumOfThreeElements function (...elements)
if (length of items > 3)
even because (i < elements.length)
Classes are syntactic sweeteners for JavaScript constructor functions as described in ES6. Classes cannot be used before they are declared; they are not like functions. Additionally, it can use extended keywords to inherit methods and attributes from other classes. An error message will appear if the strict mode (use strict) is not followed.
Function* is used to declare generator functions along with a unique class of functions and keywords. It returns a generator object and manages the execution; it does not actually run the code.
A weak set is an ordered collection of unique components that exclusively includes weakly referenced objects.
An object with keys and values is called a weakmap; if the object has no references, it is gathered as trash.
One way to extract elements from an object or array is to use object destructuring.
log(first) in console; // Outputs 1
outputs2; console.log(second);
Third Output: console.log(third); //
When variables are specified using the let and const keywords before they are initialized, a phenomenon known as the Temporal Dead Zone takes place.
Errors arising from JavaScript's repetitious approach to a given task may arise when developing JavaScript browser applications. JavaScript design patterns are the name given to this recurring methodology pattern. The Structural, Behavioral, and Creational design patterns are the types of JavaScript design patterns.
One value at a time can be displayed using the primitive data types. Data types that make up this set include Boolean, Undefined, Null, Number, and String.
The purpose of the Deferred scripts is to wait for the HTML parser to complete before running it.
In JavaScript, lexical scoping is possible when the function code and references pertaining to the current scope chain comprise the internal state of the JavaScript function object.
This is a three-dimensional array, [[[]]].
Java and JavaScript are interchangeable, yes.
Navigator can be used to identify the operating system on the client computer.string appVersion
JavaScript provides three types of pop-up boxes: Alert Box, Confirm Box, and Prompt Box.
For your interview preparation, here are a few higher level JavaScript interview questions and answers.
arr.length is equal to zero;
as long as arr.length > 0
arr.pop();
arr.length - arr.splice(0);
The outermost element's event is first captured in this procedure, and it is subsequently propagated to the innermost element.
The innermost element's event is first captured in this procedure, and it is subsequently propagated to the outermost element.
More rigorous error-checking is introduced in JavaScript code when using the strict mode.
console.log(a);
This JavaScript code will produce 10undefined as its output. The code's if condition statement uses eval to evaluate. Function abc(){} will therefore be returned by eval(function abc(){}).
Because the code for the if statement runs at runtime while the statement inside the if is being evaluated, executing typeof abc inside the if statement returns undefined.
document.createElement("p"); var newP =
"This is a new text node" is returned by var textNode = document.createTextNode;
document.getElementById("firstP").appendChild(newP); newP.appendChild(textNode);
The call() method accepts this value as well as individual arguments.
This value and an array representing the arguments are passed to the apply() method.
Since a function declaration can only contain one reference variable as its name, the result would be a reference error.
var stud1 = Student.create(Object);
get rid of stud1.college;
console.log(stud1.business);
In essence, this is a straightforward illustration of object-oriented programming. Since we are accessing the student object's property, the outcome will be ABC.
The filter() method requires three arguments in order to be called. These are the array, the current element, and the current element's index.
Each element that repeats is stored in an empty array.
We hope that these JavaScript Interview Questions and Answers have given you further insight into the kinds of questions you might be asked as you get ready for your next job interview.
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Now that you are aware of JS Interview Questions and Answers, are you wondering how you may acquire the knowledge and abilities required to capitalize on JavaScript's enormous popularity? We've got you covered! After completing our extensive post-graduate program in full stack web development, you'll be better equipped to get employment as a software engineer.
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Aryan is a tech fanatic who enjoys keeping up with the latest developments in cutting-edge technology. He is an enthusiastic technology enthusiast, an astute researcher, and an inspirational writer. He loves technology aside from playing football, which he plays regularly.
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