This information is intended for Front End Developer candidates. The list includes basic theoretical and code questions.
I hope my experience and the experiences of other developers will help you get better interview results.

P.S. My main goal is to help candidates (including myself) get more web knowledge. Let's improve the hard skills of the Front-End community together. Please send you Front-End interview questions via pull request.

1. Common interview questions
2. Common technical interview questions
3. HTML interview questions
4. CSS interview questions
5. Javascript interview questions
   • Junior candidate
   • Middle candidate
   • Senior candidate
6. Javascript Coding
7. React interview questions
8. Typescript interview questions
9. GIT interview questions
10. Testing interview questions
11. Funny questions
12. Contributing

1. What was the most interesting solution you implemented during your last project?
2. What is the last book you read?
3. How big was your team?
4. Have you ever worked in Agile, Scrum or Kanban environments?
5. Which developers do you know in the Front End community?
6. What do you do to improve programming skills?
7. What are the most common types of web attacks? - @answer--blog.sucuri.net
8. What is the difference between imperative and declarative programming in JS? - @answer--redotheweb.com

1. What is REST? - @library--restcookbook
2. What is the difference between PUT and PATCH methods in REST? - @answer--stackoverflow
3. Talk about the differences between websockets, long polling and SSE. - @answer--stackoverflow
4. What is CORS? - @answer--maxcdn.com, @doc--mdn
5. List the main things you can do to increase page speed loading? - @answer--crazyegg.com
6. Progressive enhancement vs graceful degradation. What is the difference? - @answer--w3
7. Do you use Grunt, Gulp, Webpack or Browserify in your projects?
8. What do you know about "60fps"? How can you achieve it? - @answer--github
9. What is the difference between layout, painting and compositing? - @answer--google
10. What is Web Components? - @doc--mdn
11. What is the difference between sessioStorage, localStorage and cookies? @answer--stackoverflow

1. Could you list major HTML5 tags? - @doc--mdn
2. What does an 'optional' closing tag mean? - @doc--w3
3. When and how to preload resources? - @answer--medium
4. What is the difference between id and class? - @answer--css-tricks

1. What is the difference between 'mobile first' and 'desktop first' - @answer--codemyviews.com?
2. Which of these selectors has the highest specificity. What color will be applied to the paragraph?
3. What does the pseudo-class :root refer to?
4. What preprocessor do you use? (Sass or Less)

1. Who is the author of JavaScript Language?
2. What is the best book for learning JavaScript and why? - @answer-good-js-books--github
3. What is the type of NaN? How to check if a value is NaN?
4. What the reason that window.window === window return true? - @doc--mdn
5. What is the outcome of the JavaScript calculation? 1/0 = ?
6. What is hoisting? @doc--mdn
7. What is the difference between bubbling and capturing? - @answer--stackoverflow

1. What does this refer to? - @answer--javascriptissexy
2. What is the JavaScript Event Loop? - @answer--altitudelabs.com, @video-Roberts--youtube
3. What is the Event Delegation? - @answer--davidwalsh, @code-example
4. What is the difference between e.target and e.currentTarget? - @doc--mdn, @code-example
5. What is Window.postMessage() and where it can be used? - @doc--mdn
6. Is there any difference between Promises and callbacks? Which is better? - @answer-callback--callbackhell.com,
7. What is recursion? When is the use of recursion useful in Javascript? - @answer--medium
8. What do you hear about DRY, KISS, YAGNI? - @answer-thefullstack.xyz

1. What patterns do you know and successfully use in JavaScript?
2. What is the difference between Deferred and Promise objects? Where is Deferred object used?
3. What is the problem throttling and debouncing are resolved? What is the core difference between them? - @answer--medium
4. What is SOLID? @answer-wiki
5. What is the difference between inheritance and composition? What do you prefer? Why? @answer-hackernoon.com, @answer--medium

• Write a pipefy function where a string received is returned, but with the | character between each character. Make it possible to execute function in this way: 'javascript'.pipefy(). - @code-answer
• Write a currying function that return sum of two numbers.
• Write a factorial function without side effect. @code

// Code below must return true
alert(factorial(3) === 6 && factorial(0) === 1);

• Which line of the below code will be executed with an error? Why?

10 .toString();
(10).toString();
10..toString();

• What is the order of alerts?

setTimeout(function(){
    alert('gorilla');
    setTimeout(function(){
        alert('classical inheritance')
    }, 0);
    alert('drumroll');
}, 0);

alert('banana');

• What is the result after code execution: 1, 2 or 3?

var x = 1;
var foo = {
  x:2,
  bar: function() {
    x = 3;
    return this.x;
  }
}
var run = foo.bar;

alert(run());

• What below code will return: true or false. What does each part of code return?

new String('a') instanceof String && 'b' instanceof String;

• Does a({}, 'val') & b({}, 'val') will return the same?

var a = function(obj, val) {
    obj.val = {
        a: 1,
        b: 2,
    }

    return obj;
}

var b = function(obj, val) {
    return obj.val = {
        a: 1,
        b: 2,
    }    
}

• What would be the output of this code below?

   (function () {
      console.log(a, b);
      var a = 1;
      const b = 2;
   }())

Which one of the function expression below would be the best choice for the prototype-constructor pattern (a, b, c)? Why?

function Man (name) {
	this.name = name;
}

// a
Man.prototype.getName = function () {
	return this.name;
}

// b
Man.prototype.getName = function getName() {
	return this.name;
}

// c
Man.prototype.getName = () => {
	return this.name;
}

1. What happens when you execute setState() in the render() method?
2. What is the difference between 'smart and dummy' components?
3. How to create higher order component?
4. Tell about React in the SEO context.
5. Why rendering of React Components in the custom <div id="app"> is good practice than simple to the <body>?
6. What does mean "Isomorphic React Application"? - @answer--smashingmagazine
7. What is the difference between Mobx & Redux? - @answer

1. Talk about the differences between public, private, and protected class access modifiers? @answer--typescriptlang.org

1. What is the main difference between merge and rebase? - @answer

1. Explain the difference between unit tests and integration tests? - @answer--stackoverflow
2. Tell about TDD. What advantages or disadvantages of this concept you know? @answer--wiki
3. Which frameworks/platforms do you use for test you code?
4. List unit testing best practices principles. @answer-slides

1. Do you like parties?
2. Do you know that we have a dress code?
3. Where do you see yourself in 5 years?