Frequently asked frontend developer interview questions in 2022

Frontend development is a good starting point for beginners to foray into web development. Due to the ease of learning and the option to choose from dozens of technologies, frontend is also considered the first step towards becoming a full stack developer.

HTML, CSS, and JavaScript are the skills that are mandatory for any frontend development, but that’s not enough to build a career. The journey from beginner to intermediate frontend developer also requires learning development tools and frameworks.

Being familiar with these frequently asked frontend developer interview questions will help you form a strategic plan to crack the next interview. So, let’s get started.

What is CORS? How does it work?

Cross-origin resource sharing (CORS) is the mechanism used to improve a webpage’s performance by allowing it to access resources, such as fonts, JavaScript, images, etc., from another domain. HTML5 supports CORS, which uses the XMLHttpRequest to access resources on a different domain.

Developers must include new HTTP headers for CORS, providing access to permitted origin domains. The HTTP OPTIONS request header is necessary for browsers to be able to get responses from servers. For CORS, the header must also include credentials verifying the authenticity of the request’s origin to access resources on other domains successfully.

Explain the output of the following code 

var hero = {

   _name: ‘John Doe’,

   getSecretIdentity: function (){

     return this._name;

   }

};

var stoleSecretIdentity = hero.getSecretIdentity;

console.log(stoleSecretIdentity());

console.log(hero.getSecretIdentity());

The output of the code will be:

undefined

John Doe

The first output of the code is undefined because the code extracts the method from the hero object. It is not accessible because of its local scope, so stoleSecretIdentity() is being invoked globally. However, the _name property does not exist.

To fix the issue, we will need to fix the stoleSecretIdentity() function such that it can access the method like this:

var stoleSecretIdentity = hero.getSecretIdentity.bind(hero);         

What is a Callback Hell error in frontend development, and what causes it?

Callbacks are used in JavaScript, also known as Asynchronous JavaScript. Many developers mess up the code, and their function ends up looking like this:

fs.readdir(source, function (err, files) {

  if (err) {

   console.log(‘Error finding files: ‘ + err)

  } else { 

files.forEach(function (filename, fileIndex) {  

console.log(filename)

    gm(source + filename).size(function (err, values) {

     if (err) {

      console.log(‘Error identifying file size: ‘ + err)

     } else {     

console.log(filename + ‘ : ‘ + values)

      aspect = (values.width / values.height)    

widths.forEach(function (width, widthIndex) {

       height = Math.round(width / aspect)     

console.log(‘resizing ‘ + filename + ‘to ‘ + height + ‘x’ + height)      

this.resize(width, height).write(dest + ‘w’ + width + ‘_’ + filename, function(err) {

        if (err) console.log(‘Error writing file: ‘ + err)

       })  

}.bind(this))

     }

    })

   })

  }

})

The pyramid share of the closing parenthesis ‘})’ is called callback hell in frontend development.

It occurs when a frontend developer tries to write JavaScript functions so that the execution happens visually from top to bottom. It slows down the entire code and must be avoided. Most developers from programming languages like C, Python, and Ruby commit this mistake because these languages serially execute the code line by line. So the execution happens from top to bottom.

What is a strict mode?

In ECMAScript 5, a version of JavaScript, there is the ability to declare Strict Mode. It allows developers to put code blocks in the “strict” operating context that prevents specific actions from being taken. Strict Mode is a tool that highlights potential problems in an application without rendering any visible UI. It throws more exceptions than other methods because it activates additional checks and warnings.

The typical syntax for using strict mode is like this:

// Non-strict code…

(function(){

  “use strict”;

  // Define your library strictly…

})();

// Non-strict code…

What is Coercion in JavaScript?

In JavaScript, when one build-in type is converted to another it is called coercion. It is also known as Type Coercion and is a valuable function for adding validation to the frontend elements. Compared to Type Conversion, coercion is different because it can be used in two forms in JavaScript: explicit and implicit.

Here is an example code for explicit coercion:

var a = “42”;

var b = Number( a );

a; // “42”

b; // 42 — the number!

An implicit coercion uses no type declaration:

var a = “42”;

var b = a * 1; // “42” implicitly coerced to 42 here

a; // “42”

b; // 42 — the number!

Conclusion 

Ability to deploy agile solutions and fully exploit modern frontend technologies is what employers are looking for in candidates at present. As you gain experience as a frontend developer, there will be more complex questions to answer, but as a beginner, you must focus on fundamentals.

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