Table of Contents[Hide][Show]
- 1. What does JavaScript mean to you?
- 2. Name two fundamental programming paradigms for JavaScript development.
- 3. What distinguishes JavaScript from Java?
- 4. What forms of data does JavaScript support?
- 5. What qualities does JavaScript possess?
- 6. What are the drawbacks of using JavaScript?
- 7. How does JavaScript allow you to build an object?
- 8. In JavaScript, how do you construct an array?
- 9. How to define a name function in JavaScript and what is it?
- 10. In JavaScript, describe hoisting.
- 11. What are a variable’s JavaScript scopes entail?
- 12. Which is faster, ASP script or JavaScript?
- 13. Describe how prototypal inheritance differs from classical inheritance.
- 14. Write the program that will dynamically add new components.
- 15. Callback: What is it?
- 16. How can a JavaScript program be debugged?
- 17. Closure: What is it? Give an illustration.
- 18. What methods are there for including JavaScript code in an HTML file?
- 19. How do timers in JavaScript function?
- 20. What are your views about cookies?
- 21. How would one make cookies?
- 22. What are the JavaScript variable naming conventions?
- 23. What makes let and var different from one another?
- 24. Why do self-invoking functions exist?
- 25. What distinguishes property from attributes?
- 26. In JavaScript, what do the arrow functions do?
- 27. What is a language that is typed?
- 28. In JavaScript, please describe NEGATIVE INFINITY.
- 29. What distinguishes undefined from null?
- 30. Write some JavaScript code to show how to obtain the inner HTML of an element.
- 31. What are some of the JavaScript frameworks?
- 32. In JavaScript, what is an event bubbling?
- 33. What does JavaScript memoization mean?
- 34. What do imports and exports mean?
- 35. What is JavaScript’s “Strict” mode, and how is it activated?
- 36. What accomplishes the operator instanceof?
- 37. In JavaScript, what does a prompt box mean?
- 38. In JavaScript, what does a generator do?
- 39. BOM: What is it?
- 40. Deferred scripts: What function do they serve in JavaScript?
- Conclusion
A free and open-source programming language is JavaScript. It is meant to be used to create web-based applications. It is lightweight and interpretable, which makes it much faster than other languages.
It is easier to employ JavaScript in web applications because of its HTML integration. To determine how crucial it is, disable JavaScript in your browser and try to load the page.
These websites won’t function correctly. Their contents frequently behave poorly. Almost all modern browsers mix HTML, CSS, and JavaScript.
JavaScript is one of the interpreted programming languages. An interpreter is already included in many browsers, including Google Chrome, Microsoft Internet Explorer, and others.
Thus, its code can be processed by the browser’s JavaScript Engine. Here is a beginner to expert-level JS interview questions and answers for your reference if you are prepared for an interview.
The purpose of the same is to introduce you to the types of questions you can encounter during your technical interview. Let’s begin.
1. What does JavaScript mean to you?
The most used web scripting language, used for both client-side and server-side programming, is JavaScript. JavaScript code can be placed into HTML pages that web browsers can comprehend and execute, supporting the capabilities of object-oriented programming.
2. Name two fundamental programming paradigms for JavaScript development.
Programming with JavaScript, a multi-paradigm language, allows for:
- procedural/imperative programming
- Object-oriented programming (OOP)
- Using functional programming
- A prototype-based programming approach or a prototype-based inheritance (an extension of OOP)
3. What distinguishes JavaScript from Java?
While JavaScript is primarily a scripting language, Java is a programming language. Java is a programming language used by developers to create programs that can run on a computer’s operating system, virtual machine, or web browser. In contrast, JS code is designed to only run within a browser.
But utilizing Electron and Node.js, independent desktop apps can be created in JavaScript. Java and JS code differ significantly in that the latter is available in text format, while the former requires compilation.
4. What forms of data does JavaScript support?
Data types that JavaScript supports include:
- String
- Symbol
- Number
- Object
- Undefined
- Null
- Boolean
5. What qualities does JavaScript possess?
It is a free and universal scripting language.
It is an interpreted programming language that is lightweight.
It is intended to be used to build network-centric applications.
Both are connected and complementary to Java.
6. What are the drawbacks of using JavaScript?
Coders with experience will be able to discuss the shortcomings of their preferred language in addition to extolling its virtues. Security is JavaScript’s worst flaw. Seek information on how it can be abused.
A further drawback of JavaScript is its widespread use and adaptability, which can be a double-edged sword because it leaves a lot of leeway for programming oddities that could result in uneven performance on various systems.
7. How does JavaScript allow you to build an object?
The idea of objects is well-supported by JavaScript. Using the object literal, you can build an object like seen below:
8. In JavaScript, how do you construct an array?
The array literal can be used to define arrays as follows:
9. How to define a name function in JavaScript and what is it?
When a named function is defined, it immediately defines a name. It can be described as follows using the function keyword:
10. In JavaScript, describe hoisting.
All variable and function declarations are shifted to the top by default in JavaScript, which is known as hoisting. This implies that all variables and functions, regardless of where they are defined, are relocated to the top of the scope. The reach might be local or international.
11. What are a variable’s JavaScript scopes entail?
The section of your program where a variable is defined is the variable’s scope. There are only two scopes that a JavaScript variable can have.
- Global variables: Everywhere in your JavaScript code can see a global variable since it has a global scope.
- Local variables: Only within the function in which it is declared will a local variable be visible. Local to that function, function arguments are always present.
12. Which is faster, ASP script or JavaScript?
Faster is JavaScript. JavaScript can be executed without the help of the web server because it is a client-side language. However, as ASP is a server-side language, it will always be slower than JavaScript. Currently, JavaScript is also a server-side language (nodejs).
13. Describe how prototypal inheritance differs from classical inheritance.
JavaScript has the wonderful ability to do away with the strict constraints of traditional inheritance and allow objects to inherit attributes from other objects. –
- Classical Inheritance:With the help of the “new” keyword, a constructor function creates an instance. A parent class’s attributes are passed down to this new instance.
- Prototypal Inheritance: An existing object that acts as a prototype is copied to generate an instance. Selective inheritance from a wide variety of objects might be advantageous for this instance, which is frequently created via a factory function or “Object.create()”.
14. Write the program that will dynamically add new components.
15. Callback: What is it?
A simple JavaScript function sent as an argument or option to a method is known as a callback. The term “call back” refers to a function that is intended to be performed following the completion of another function. Functions are objects in JavaScript. JavaScript objects are functions. Functions can therefore return other functions and receive other functions as inputs.
16. How can a JavaScript program be debugged?
By hitting the relevant key, usually, the F12 key, all contemporary web browsers, including Chrome, Firefox, and others, come with an embedded debugger that can be used at any time.
Users can make advantage of a variety of features offered by the debugging tools. A code editor that we use to create JavaScript applications also allows us to troubleshoot JavaScript code.
17. Closure: What is it? Give an illustration.
When a variable specified outside the current scope is accessed from a scope that is inside it, closures are produced. It allows you to access the scope of an outside function from an inside function.
Every time a function is generated in JavaScript, a closure is also produced. Simply write a function within another function, expose it, then utilize it to implement a closure.
18. What methods are there for including JavaScript code in an HTML file?
JavaScript code can be inserted primarily in one of two ways:
- When only a few lines of scripting are required within a web page, we can write JavaScript code within the script element in the same HTML file.
- To add all scripting features to a web page without clogging up the code, we can import a JavaScript source file into an HTML document.
19. How do timers in JavaScript function?
Timers are used to run or repeat a piece of code at a predetermined time. The setTimeout, setInterval, and clearInterval methods are used to do this.
Using the setTimeout(function, delay) function, a timer that runs a certain function after the specified delay is set up. The function setInterval(function, delay) repeatedly runs the specified function in the specified delay and only stops when canceled.
The timer is told to end using the clearInterval(id) method. Because timers are run on a single thread, events can queue up and wait to be performed.
20. What are your views about cookies?
A cookie is often a little piece of data that a website sends to the user’s computer and that is saved there by the web browser that was used to visit the page.
Cookies are used to capture website viewing activities and to remember information for later use.
21. How would one make cookies?
The following is the simplest JavaScript method for generating cookies:
22. What are the JavaScript variable naming conventions?
When naming variables in JavaScript, you must adhere to the following rules:
Any JavaScript reserved keywords should not be used as variable names. For instance, variable names ending in break or boolean are invalid.
The name of a variable in JavaScript shouldn’t begin with a number (0-9). They have to start with a letter or the underscore symbol.
For instance, 123name is not an acceptable variable name, although _123name or name123 is. Case matters in JavaScript variable names. Test and test, for instance, are two distinct variables.
23. What makes let and var different from one another?
In JavaScript, declarations of variables and methods can be made using either let or var. The only real distinction between these two is that the let keyword is scoped by a block, whereas the var keyword is scoped by a function.
24. Why do self-invoking functions exist?
Immediately Invoked Function Expressions or Self Executing Anonymous Functions are other names for them. These are known as “Self Invoking Functions” since they are called by the code automatically.
We write a function and call it. However, anonymous functions might be used if we want a function to run automatically when it is explained and if we won’t be using it again. Additionally, some functions lack a name.
25. What distinguishes property from attributes?
The attributes of JS DOM objects function similarly to instance variables for certain components. Property can include a variety of data kinds.
You can access properties by interacting with the object in Vanilla JS or by using the prop() function of jQuery.
Attributes are found in the HTML, not the DOM. They are comparable to properties but have less capability. If properties are available, working with them is advised over working with attributes.
An attribute is a string data type, as opposed to property.
26. In JavaScript, what do the arrow functions do?
In JavaScript, arrow functions are a quick and clear method to write functions. An arrow function has the following general syntax:
27. What is a language that is typed?
Values rather than variables are related to each other in typed languages. There are two categories:
Dynamically: Unlike in JS, where a variable can accept a number or a string, this allows the variable to contain many kinds.
Statically: In this, a variable can only store one type; for example, in Java, a string variable can only store a certain set of characters.
28. In JavaScript, please describe NEGATIVE INFINITY.
When a negative integer is split by 0, the static property NEGATIVE INFINITY that results is created in JS. These are some of its crucial traits:
No additional objects must be created in order to access NEGATIVE INFINITY.
The NEGATIVE INFINITY property’s value corresponds to the infinity property’s negative value for the global object.
29. What distinguishes undefined from null?
Undefined denotes a declared variable that has not yet been given a value. Null is an assignment value, on the other hand. It can be used to indicate no value and be assigned to a variable.
Undefined is a type in and of itself (undefined), whereas null is an object. Undefined and null are also two different kinds.
30. Write some JavaScript code to show how to obtain the inner HTML of an element.
31. What are some of the JavaScript frameworks?
An application framework created in JavaScript is known as a JavaScript framework. In terms of control flow, it varies from a JavaScript library. There are several JavaScript frameworks available, however, a few of the more popular ones include:
- Angular
- React
- Vue
32. In JavaScript, what is an event bubbling?
When an event happens in one element inside another element and both elements have registered a handle for that event, the HTML DOM API uses event bubbling as a method of event propagation.
When there is bubbling, the event is initially detected and processed by the innermost element before being passed on to the surrounding components.
Beginning with that event, execution moves to its parent element. Following that, its parent element receives execution, and so on until the body element.
33. What does JavaScript memoization mean?
Memorization is an optimization method that speeds up your code by saving the outcomes of pricey function calls and reusing them when the same input is received again.
A function is referred to as being costly if it requires a lot of time and memory to execute because it performs complex calculations. A cache is promptly populated with the outcome of an expensive function call.
The same function will bypass the necessary computation and return the cached value if it is called again with the same input parameters.
Because the function doesn’t need to redo any calculations or computations it has already performed, this method dramatically saves the time and memory your program uses.
34. What do imports and exports mean?
We can create modular JavaScript code with the aid of imports and exports. We can divide our code into several files by using imports and exports. Examples include
35. What is JavaScript’s “Strict” mode, and how is it activated?
You can improve error-checking in your code by using strict mode.
When using strict mode, you are unable to add properties to non-extensible objects, assign values to read-only properties, utilize implicitly declared variables, or assign values to read-only variables.
By beginning a file, program, or function with “use strict,” you can activate the strict mode.
36. What accomplishes the operator instanceof?
The instanceof operator determines if an object’s prototype chain has any instances of a constructor’s prototype property. In other words, the instanceof operator determines at runtime if an object is an instance of a class.
The instanceof operator is used in the example below to determine the type of variable users.
37. In JavaScript, what does a prompt box mean?
A prompt box is a box with a text box that allows the user to provide input. A dialog box asking for input is displayed via the prompt() function. Use a prompt box if you need the user to enter a value before seeing a page.
The user must select “OK” or “Cancel” in the popup box that appears after inputting a value to continue.
38. In JavaScript, what does a generator do?
Generators are functions that can be used at different times. The context and variable bindings of these functions are saved and maintained throughout re-entrances.
A generator function’s initial call returns a particular kind of iterator called a generator. The next step is to call the generator’s next method to use the value. Until it comes across the yield keyword, the generator function keeps running.
39. BOM: What is it?
The BOM, or browser object model, allows users to interact with browsers, with which a window serves as the first object. In addition to other features, the window object has a document, history, screen, navigator, and location.
The window’s function, however, can be accessed both directly and by referencing the window.
40. Deferred scripts: What function do they serve in JavaScript?
The browser starts to parse the HTML code when a page loads. By default, the browser pauses parsing HTML code when it encounters a script and begins running the script instead.
Following the script’s completion, the browser resumes processing the HTML code.
The page load will be delayed by a sluggish server or a large script. Deferred scripts put off running the script until after the document has been processed.
This delay in the script’s execution reduces the time it takes for the webpage to load.
Conclusion
We hope these JavaScript interview questions will be helpful to you, whether you’re a developer getting ready for a meeting or a hiring manager trying to find the right applicant.
Remember that technical expertise and knowledge make up just a small portion of the recruiting process. To ensure that you land (or locate the suitable applicant for) the job, past experience, and soft skills are equally crucial.
Be aware that there are frequently several right answers to open-ended JavaScript interview questions. Interviewers are interested in the reasoning behind your responses, not just the answer you memorized.
Be ready for follow-up inquiries about how you arrived at your response and always be able to explain your thought process.
Check out Hashdork’s Interview Series for help with interview preparation.
Arun
Wow, This article helped me a lot during my Javascript Interview preparation