The demand for a Frontend developer is continuously increasing in this digital age. However, one needs to master various skills for it, including programming skills like HTML, CSS and JavaScript.Yet, there is still one major obstacle that filters out many aspirants, and you must prepare for it.
Yes, you are correct, it is the interview. It is one of the major filters recruiters use to know whether a candidate is a good fit for the job or not. This blog will guide you on cracking the Frontend developer interview by practising common interview questions and their ideal answers.
20 Commonly Asked Frontend Developer Interview Questions And Answers
1: What is the difference between HTML, CSS, and JavaScript?
Recruiters prefer candidates to have information about what is HTML, CSS and JavaScript. However, they can stand out from other candidates through their knowledge of the difference between HTML, CSS and JavaScript.
| HTML | CSS | JavaScript |
|---|---|---|
| Structured language | Stylish sheet language | Programming language |
| Used to structure the content of a web page | Used to describe the presentation of a document written in HTML | Used to make web pages interactive and dynamic |
| Requires checking by a compiler. | Doesn’t need to be checked by a compiler. | |
| Gives the basic framework for web pages, defining elements such as headings, paragraphs, images, links, and lists | Separates the content of a web page from its design, making it easier to maintain and update the appearance of a website | Manipulate HTML elements, modify content, respond to user actions (such as clicks and keystrokes), and create animations and effects |
2: Explain the box model in CSS.
The box model in CSS is an important concept in Frontend development. It describes all elements of HTML and has multiple properties, including border, margin, padding, and center. It is primarily useful for creating the layout of a web page.
Here’s how the box model in CSS looks like:
3: What is semantic HTML? Why is it important?
Semantic HTML refers to using HTML elements according to their meaning. It defines the different sections and layout of the web page in a better way. Tags like <header> <body> <footer> etc., are semantic HTML tags that are useful to define a web page.
This definition is suitable to both humans and machines like search engines alike. Semantic HTML helps convey the correct meaning of content, which is especially useful for users with special abilities who rely on screen readers or other assistive technologies. Additionally, search engines can better understand the content and context of a page, which can boost SEO.
4: What are the new features of HTML5 and CSS3?
HTML5 and CSS3 have introduced new features helpful for the Frontend developer to build and maintain a website layout. Here are some of the key features.
HTML5
- HTML tags like <header> <footer> <article> <section> and <side> are available to improve the structure of web documents.
- Supports embedding of audio and video using <audio> and <video> tags.
- Supports Scalable Vector Graphics using the <SVG> tag.
- HTML5 allows users to mark up a photo using <figure> element and define its caption with <figcaption> tag.
CSS3
- Developers can create shadow effects with Box Shadow and Text Shadow.
- Developers can easily round the corners of an image and block elements.
- Developers can use rbga colours to reduce the opacity of the background and elements.
- Developers can animate any object on the web page without any need to use Flash.
5: What is responsive web design? How you can achieve it?
Responsive web design is an approach that makes a web page render flawlessly across various devices having screens of different sizes. Its purpose is to provide an interactive viewing experience to the users along with easy-to-use navigation. As a developer, you can easily create a responsive web design using the following tips:
- Allow layout to adapt and scale flawlessly on different screen sizes using relative units instead of fixed units.
- Apply different styles according to the characteristics of the device like screen width, height, or orientation.
- Enable the browser to control the dimension and scaling of a web page using the Viewport tag.
- Use <picture> element to define different images for different browsers’ window sizes.
6: Describe the difference between “inline, block, and inline-block elements in CSS.
Many Frontend developers struggle to understand the difference between “inline, block, and inline-block elements in CSS. These developers can learn about it from the differences given here:
“inline”
Inline elements in CSS do not start on a new line and take as much width as necessary. Its examples include <span>, <a>, <strong>, <em>, <img>, <input>, and <br>.
“block”
Block elements start on a new line and take up the full width available to them. Its examples include <div>, <p>, <h1> to <h6>, <ul>, <ol>, <li>, <table>, <form>, and <blockquote>.
“inline-block”
Inline-block elements are similar to inline elements with the difference that they can take up specific height and width.
7: What are CSS preprocessors? Name a few examples.
CSS preprocessors are popular tools that extend the functionality of CSS by adding new-age features like variables, nesting, functions, mixins, etc. These preprocessors allow Frontend developers to write more maintainable and modular CSS code by using features that are not natively available in CSS. Some of its examples are given below.
- SASS or Syntactically Awesome Stylesheets
- LESS or Leaner Style Sheets
- Stylus
- Syntactically Awesome Style Sheet CSS or Sassy CSS
8: Explain the concept of CSS specificity.
Specificity is the advanced algorithm used by many browsers to define the CSS declaration that will be most appropriate to HTML elements. It is a set of rules that helps determine which CSS styles are applied to an element when multiple conflicting styles are targeting the same HTML element. It calculates the weight that is applied to the gives CSS declaration.
9: What are pseudo-classes and pseudo-elements in CSS? Provide examples.
Answer: Pseudo-classes and pseudo-elements are CSS selectors that allow all Frontend developers to target elements based on their state or position in the document tree. It eliminates the need to add additional classes or IDs to the HTML.
Pseudo-classes
This selects the elements in CSS and modifies the state of the element according to user interaction. They always start with a colon and include these common pseudo-classes examples.
- :hover – It is useful to style elements when the user hovers over it.
- :active – It is useful to style elements when activated by the user.
- :focus – It is useful to style elements when it has a focus.
- :not(selector) – It is useful to select elements that do not match a specific selector.
Pseudo-elements
Developers use it to style certain parts of an element. It begins with a double colon and includes these common pseudo-elements examples.
- ::before – It is useful to insert content before the content of an element.
- ::after – It is useful to insert content after the content of an element.
- ::first-line – It is useful to style the first line of text within an element.
- ::first-letter – It is useful to style the first letter of text within an element.
10: What is the purpose of a CSS reset? Do you prefer using a reset or a normalize .css file?
A CSS reset is a set of CSS rules that aim to reduce browser inconsistencies by resetting the default styles applied by browsers. The purpose of CSS reset is to provide a clear slate for styling. It ensures that elements behave more consistently across different browsers. However, the choice between a reset and normalize.css ultimately depends on the specific requirements and goals of your project.
11: What is the difference between `==` and `===` in JavaScript?
A Frontend developer should have information about equality operators like doubt equals (==) and triple equals (===). These are useful to compare two values, however, both operators perform different jobs.
Equality (==): This operator first converts two values to a common type and compares them for equality.
Strict Equality (===): This operator compares two values without using type conversion. If the types of the two values are different, the comparison will return false without attempting to convert the values.
12: What are closures in JavaScript?
In JavaScript, closures are functions that have access to the outer (enclosing) function’s variables, even after the outer function has finished executing. This behaviour is possible because JavaScript functions are first-class objects, which means they can be passed around like any other object.
13: Explain the concept of event bubbling and event capturing in JavaScript.
When developers build web pages, they use the concept of event-bubbling. In this, event handlers are invoked when one element is nested on the other one. Here, both these elements are part of the same event. This is known as event bubbling.
Whereas event capturing is just the opposite of event bubbling in which the event moves from the outermost element to the target. Event capturing is performed very rarely and it always comes before event bubbling.
14: What is AJAX? How does it work, and what are its advantages?
AJAX or Asynchronous JavaScript and XML is a set of techniques for web development (Frontend and Backend Development) used to create asynchronous web apps. It allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes. It means that the user doesn’t need to reload web pages every time.
Here’s how AJAX works:
- User interaction with a web page by clicking a button or submitting a form.
- JavaScript event listener captures the user’s interaction and triggers an AJAX request.
- AJAX request is sent to the server using the XML HTTP Request object or the fetch API.
- Server-side processing processes the request, such as querying a database.
- The server sends a response back to the client, in the form of JSON or XML.
- Once the response is received, JavaScript processes the data and updates the web page dynamically.
Advantages of using AJAX:
- Update content on the webpage without the requirement to reload the complete web page.
- Reduce server load and faster response time by updating only the required data.
- Encourage user interaction with the web page while the request is being processed.
- Send and receive small amounts of data for more bandwidth-efficient requests compared to traditional web requests.
- Support all modern web browsers and can be easily used with a variety of server-side technologies.
15: What are promises in JavaScript? How do they differ from callbacks?
Promises are JavaScript objects that represent the completion of an asynchronous operation. It facilitates a more powerful way to handle these operations compared to traditional callback functions. Promises have 4 states: fulfilled, rejected, pending and settled. There are 3 major differences between Promises and Callbacks, that are given here.
| Properties | Promises | Callbacks |
| Readability | Promote a more readable syntax, when combining multiple asynchronous operations. | The syntax is difficult to read and understand. |
| Error Handling | Easier to manage | Difficult to manage |
| Callback hell | Resolves callback hell | Generate callback hell |
16: Explain the difference between `null`, `undefined`, and `NaN` in JavaScript.
`Null`, `Undefined` and `NaN` are special values in JavaScript that are useful to showcase different states of variables.
| Properties | `Null` | `Undefined` | `NaN` |
| Type | Object | Undefined | Number |
| Meaning | Developers use it to indicate that a variable should have no value. | Developers use it to declare variables but have yet to be assigned a value. | Developers use it to represent that the result of an operation depends on mathematical calculations that have no value. |
| Use | Assign this value to a variable to indicate that it is empty or should not point to any object. | Variables that are declared but no value is assigned to them use undefined. | It occurs due to an arithmetic operation on any value that is not a number. |
17: What are the differences between `let`, `const`, and `var` in JavaScript?
JavaScript enables a Frontend developer to declare variables with the let`, `const`, and `var` keywords. However, all of them have different properties and behaviours. The differences between these JavaScript keywords are explained below.
| Properties | `let` | `const` | `var` |
| Scope | Block-scope | Block-scope | Function-scope |
| Hoisting | Not hoisted and initialized | Not hoisted and initialized | Hoisted and initialized |
| Redeclaration | Not allowed (within the same scope). | Not allowed (within the same scope). | Allowed |
18: What is the DOM (Document Object Model)? How do you access and manipulate it using JavaScript?
DOM or Data Object Modelling is a popular programming interface for web documents. It presents the document structure as a tree of objects. This means that it enables the programming language to interact with a document in a structured way.
A developer can access and manipulate it through JavaScript using the following process.
Selecting Elements
- ByID
- ByClassName
- ByTagName
- Via Query Selector
After selection of elements, a developer can easily manipulate it through:
- Changing Content
- Changing Attributes
- Changing Styles
- Adding or Removing Elements
- Event Handling
19: What is the difference between `localStorage` and `sessionStorage` in HTML5?
Both localStorage and sessionStorage are part of HTML5 and allow anyone to store data within a user’s browser. Some of the significant differences between them are given here:
| Properties | `localStorage` | `sessionStorage` |
| Data Status | Stored data remains available even after the browser is closed and reponed. | Stored data is temporary and is only available till the browser remains open. |
| Data Accessibility | Data stored is accessible from any page with the same origin. | Data is lost when a new tab or window is opened. |
| Storage Limit | The storage limit is up to 5-10 MB of data per origin (this limit can vary slightly between browsers). | The storage limit is around 5-10 MB (this can vary between browsers). |
20: What tools and techniques do you use for debugging and optimizing web performance?
You need to provide an adequate answer to this question during the interview of a Frontend developer like this.
To ensure optimal performance and efficient debugging of web applications, you use a combination of various tools as given below.
For Debugging:
- Chrome DevTools
- Visual Studio Code (VSCode)
- PyCharm Debugger
- Android Studio
- dbForge SQL Tool
For Performance Optimization:
- Lighthouse
- WebPageTest
These tools help identify issues and optimize performance to ensure a flawless user experience.
Conclusion
By providing a comprehensive list of common interview questions and answers, this blog aims to equip you with the necessary information regarding the interview of the Frontend developers. For further reading and continuous learning as a Frontend developer, join CodeSquadz’s full stack development training program today. It will help you access additional resources and practise regularly to stay ahead in this dynamic field.
