Front End Engineer Interview Questions

What Are Form Control And Form Groups

Form Control

• It enables validation through the Form Control class.
• It produces a new instance of this class for each input field.
• These instances allow you to verify the field’s values to see if they’ve been touched, untouched, or dirty.

Form Group

• A group of controls is represented by the FormGroup class.
• Multiple control groups are possible in a form.
• If all the controls are valid, the Form Group class returns True.
• It also includes a list of all validation problems.

Sample Interview Questions And Answers

Here are some example interview questions for front-end developers, advice on the best way to answer them and sample answers. Keep in mind that the interviewer is interested in your answers but also in your overall communication ability.

• Name three ways to reduce a page’s load time.

• How do you optimize a website’s assets?

• Explain the difference between a GET and POST request.

• Is CORS important? Why or why not?

• How do you structure your code in terms of making it possible for another coder to make changes if needed?

• Where do you see yourself in the company after your first year?

• What skills are needed to be a good front-end developer?

Explain The Javascript Event Loop

JS has a call stack that everything synchronously goes into. When you hit a function that there is a Web/Browser/Node APIs for , JS will pass that to the Web/Browser/Node APIs to handle. When they are done being evaluated they get pushed back to the callback queue. The callback queue is a queue of all the callback functions that are ready to be executed. If the call stack is empty js will look at the callback queue to execute those callback functions.

If there is a promise they will be pushed into a microtasks queue. This queue works a lot like the callback queue but is given priority over the callback queue. This means if you had an async call and a setTimeout the async callback will get executed before the setTimeout.

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What Resources Do You Use To Learn About The Latest In Front End Development And Design

Technology and standards change constantly in front end development. Applicants who have an always-be-learning approach can learn new ways to improve the development process and improve the experience for end users. What to look for in an answer:

• Examples of publications the applicant reads
• Participation in open source or personal front end development projects
• Enrollment in continuing education workshops or online courses

Example:

I have several subscriptions to front end development magazines and participate on the Stack Overflow forums. These resources help me learn about the latest innovations in front end development.

Front End Engineer Interview Questions

A front end engineer is focused on the user experience of software or an app. During an interview, you will need to demonstrate that you understand UX/UI design principles, a commitment to clean code optimized for the product offering, and a willingness to work with backend engineers to solve problems. Expect to be asked about your technical experience, as well as your people management and design skills.

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What Is A State In React How Do You Implement It

A state is an object that stores the values of properties belonging to a component that could change over a period of time.

Here are a few features of a State –

• You can change a state as a result of a user’s action or changes in the network.
• React re-renders the component to the browser whenever the state of an object changes.
• You initialize the state object in the constructor.
• It can store multiple properties in the state object.
• this.setState is used to alter the state object’s value.
• The setState function merges the new and old state and the previous state in a shallow merge.

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How Do You Structure Your Code In Terms Of Making It Possible For Another Coder To Make Changes If Needed

The employer wants to know that you’re familiar with the coding standards that apply in implementation processes. As front-end developers commonly work on code created by other developers, it’s important that you have a system in place to make it much easier on those working on code you wrote.

Example:”I begin by dividing the style sheets into sections for each of the site’s components. Each section has my notes and comments written throughout the code so other developers can understand my thought process and make changes without too much trouble.”

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Advanced Level Front End Developer Interview Questions

List of front end engineer interview questions for advanced level developers and engineers. Questions for senior developers need to be highly practical as you want to understand how the person would handle highly technical parts of a project. There is an implicit assumption that senior developers are well-versed in the basics already. So, you need not bother with those sorts of questions.

How and when can you use JavaScript functions?

The most common JavaScript functions include .forEach, .map, .filter, .reduce and .find.

• The forEach function is used in for loops to make the code more easily readable.
• The map function is for transforming and creating new arrays
• The reduce function eliminates other elements from an array to reduce it to a single value.
• The filter function is used to create new arrays with the callback feature
• The find function is used to determine the value of the first element in an array that fulfills an established condition.

What are HTTP methods and how are they used?

Take note that these are two frontend interview questions fused into one. Pay attention to how the candidate answers each part. HTTP methods are requests to specify the performance of a certain action and facilitate smooth interaction between the client-side and the server-side. Most of these methods are verbs. Hence, they are commonly known as HTTP verbs. Some of the most popular methods include:

What are the benefits of using a CDN?

What Is A Sql Injection

Another type of attack. If you have a search form, for example, and when a user types in a name like “Kelly” you take that string and do an SQL lookup for it. Let’s say your SQL looks like this:

`SELECT * FROM Users WHERE UserId = yourVariable`

An attacker could put something malicious in the search bar like `Kelly OR 1=1`, and now it will return a list of all users instead of just the requested one.

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Q5 What Are Aot And Jit Compilations

AoT compilation refers to Ahead of Time compilation, where code translation occurs while the code builds and not when itâs downloaded or run in the browserâ increasing the content tendering speed.

JiT compilation refers to Just in Time compilation, where the computer code is converted into machine code during code execution .

If you want exclusive tips to crack the Front-end interview, here are 6 steps to crack the Front-end interview.

What Do You Understand By Semantic Html How Does It Work

Semantic HTML is a type of coding that uses HTML markup to reinforce the semantics or meaning of the information in web pages and web applications rather than merely to define its presentation or look. Semantic HTML is processed by traditional web browsers and many other user agents. It is used to emphasize the content’s semantics or meaning.

The tags are different in semantic HTML as compared to normal HTML. For example, the < b> < /b> tag is not used for bold statements in semantic HTML, and the < i> < /i> element is for italic. Instead, we use the < strong> < /strong> tags and < em> < /em> tags respectively.

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What Is Virtual Dom And How Does It Work

The virtual DOM is a JavaScript version of the actual DOM that is saved in memory and syncs with the actual DOM to make things react on the page. Through libraries you are able to make JavaScript manipulate the actual DOM based off the state you want and define in JavaScript. The libraries do this by using an algorithm that looks at the difference between the state you want and the state of the actual DOM in a tree structure . It will update anything that is different and the children below it if necessary.

What Is Your Philosophy On Reusable Components Vs Simplicity And Premature Optimization

Note: this questions answer is more subjective than most of the other questions. These are the things I and all my teams in the past have looked for.

We always want to make components small and reusable but we dont want to get carried away. Simplicity and readability are key. Dont overcomplicate if you dont have to. Generally make it reusable when you need to but keep reusability in mind when creating it.

There are components you know even in the beginning stages of your application will be reused. For instance, navigation, maybe a dropdown, or a table component, or pagination. If the component is super specialized then it likely wont be reused but try to make it as reusable as possible. Think about ways it can be reused if possible but if it adding too much extra complexity just build it for what needs to be done at the time. Sometimes making something reusable makes it too complex, bug prone, and hard to support. If that is the case look into ways to make it simpler or make a new component to support some edge cases.

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Frontend Developer Interview Key Areas

These are definitely the most important areas you should expect during a frontend interview in 2021:

• Very good understanding of JavaScript that one is quite obvious. Aside of the language itself, you should be familiar with static code analysis tools.
• Good knowledge of top frameworks/libraries : React, Angular, Vue.js etc.
• HTML5 and CSS writing semantically correct HTML, pixel perfect implementations of designs into CSS, attention to detail, responsive web design.
• English you should be able to communicate fluently and make your points clearly.
• Browsers practical knowledge of browsers, how they work and how to debug your code in the browser.
• Practical experience working with APIs .
• Experience in working with GIT repos.
• Experience in writing tests.

What Skills Are Needed To Be A Good Front

How you answer will let the employer know what skills you possess yourself. They’re also looking for a confident answer, so don’t hesitate to name the top developer skills, according to you.

Example:”Any professional front-end developer should have a good understanding of HTML, CSS, JavaScript, HTTP/URL, DOM, CMS and web browsers, at least. It’s also important to be a good communicator when it comes to leaving notes in the code for later use, writing progress reports for stakeholders and explaining project details to the team.”

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What Do You Know About The Css Image Sprites And Why It Is Utilized

CSS image sprites assist to render numerous images in a single line image. In a nutshell, the CSS sprites merge numerous photos into a single large image. If a web page comprises different images, then it would raise its loading time as for every image the browser has to send a distinct HTTP request, but with the help of sprites, we have a single image to request.

Explain The Prototype Design Pattern

The Prototype Pattern creates new objects. But the peculiarity is that instead of creating non-initialized objects, it returns objects that are initialized with values copied from a prototype – or sample – object.

One example is the initialization of business objects with values that match the default values in the database. Classical languages rarely use the Prototype pattern, but JavaScript being a prototypal language uses this pattern in the construction of new objects and their prototypes.

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General Tips For Front End Interviews

Regardless of which type of format you are given, one thing stays true – you need to be extremely strong in your front end fundamentals and constantly display mastery of them to your interviewer.

Be extremely familiar with the following concepts:

• CSS: Specificity, Box model, Layout, Positioning
• JavaScript: this keyword, Prototypes, closures, Async-style code, Promises, Timers
• JavaScript design patterns: Observer pattern, Module pattern
• HTML: Event delegation , DOM traversal, DOM manipulation, Form validation and submission
• Vanilla JS, or jQuery at the very least. Not all interviews allow you to use React as they want to see mastery of the fundamentals

Look out for interview questions by companies on Glassdoor. Front end questions are not as abundant but some still can be found. Many companies use similar questions.

Clarify Ambiguities Early In The Interview

Candidates who spend time clearly defining the problem before they jump into coding have a much better chance of success. After all, front end development can be tricky or ambiguous. You should restate your understanding of the problem to your interviewer and ask any clarification questions you may have. Doing so ensures not only that you correctly understand the basic requirements of the question, but also highlights your communication skills and ability to reason through a problem with a teammate.

Another significant benefit of clarifying ambiguities before you jump in is demonstrating that you are capable of user centered design. That is, as the name suggests, a design approach in which the focus is entirely on the users and their needs. In this case, the interviewer is acting as a stand in for the user.

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What Are The Different Ways To Hide An Element Using Css

display: none

Hides the content and doesnt store it in the DOM

visibility: hidden

It adds the element to the DOM and takes up space. However, it is not visible to the user

position: absolute

You can make the element appear outside the screen

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Tell Me When And Why Should I Make Use Of Webpack

While creating a complicated front-end application with tons of non-code static possessions, for instance, CSS, fonts, images, etc, then, of course, you should make use of Webpack since it has a lot of amazing benefits.

If you have a small application that doesn’t have a lot of static resources and you only have to create one file of JavaScript to help the customers, then Webpack should be more overhead than needed.

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What Are The Benefits Of Using Coffeescript Over Javascript

Following are some key advantages of CoffeeScript over JavaScript:

• CoffeeScript is a lightweight programming language that compiles into JavaScript.
• CoffeeScript contains a lot of lightweight add-ons like Ruby string Interpolation and Python style list comprehension.
• CoffeeScript facilitates developers to express their programs with a lot shorter code than JavaScript.
• CoffeeScript makes the JavaScript code good and more readable.
• It is easy to perform everyday tasks with CoffeeScript rather than JavaScript.

Suggest Some Ways On How To Fix The Browser

• We can make a distinctive stylesheet for various browsers making use of server-side rendering.
• Another method is utilizing a library such as Bootstrap, which already has the code to manage the browser-specific styling issue.
• Reset or Normalize CSS can also be utilized. Multiple 3rd party plugins equip libraries for browser styling issues.

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Fronted Interview Questions Summary

What do you think about the questions and advice? Are you now ready to try your luck? Remember:

• Make sure to prepare yourself extremely well when it comes to technologies that are your strongest suit. You dont have to be good at everything though.
• During a typical interview, you will be asked to solve some practical cases. Learning definitions by heart is not a good idea. Get familiar with frontend interview questions, but think of them as nothing more than a guideline.
• Take the initiative and show the recruiters your own projects, ask them your own questions about the company and your role too.

Witold Ossera

Head of Frontend Team

Adrian Senecki

Content Creator

Mention The Difference Between Mysql And Mongodb

• MySQL: It is a Relational Database Management System , which makes use of SQL as a standard language to handle its database. Like different relational database management systems, MySQL makes use of a table-like structure to stow data.
• MongoDB: MongoDB is a NoSQL database that utilizes the JSON-like structure to stow data elements. To modify and access data in MongoDB, the programmer ought to make use of the MongoDB Query Language .

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What Is The Key Difference Between Class And Prototype

The most important difference between class-based and prototype-based inheritance is that a class defines a type that can be instantiated at runtime. On the other hand, a prototype is itself an object instance. In JavaScript, the object system is prototype-based, not class-based. That’s why inheritance in JavaScript is different from other programming languages.

Objects are just a collection of name and value pairs in JavaScript. In JavaScript inheritance, there is only one construct, called object. Every object has private property linked to another object known as its prototype.

What Is A Marquee In Html

In HTML, a marquee is a scrolling piece of text displayed on the webpage. According to the marquee settings, it is either scrolled horizontally across or vertically up or down your web page. The marquee effect is created by using HTML < marquee> tag, which automatically scrolls the text or images up, down, left, or right.

Note: The < marquee> tag is now deprecated in HTML5. You can use JavaScript and CSS to create such marquee effects on the new web pages.

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