JS interview questions / track of answers

JS interview questions / track of answers

https://www.sololearn.com/Discuss/1434801/?ref=app

Hethal

Dmitriy Chumikov

can some one post answers for this questions? :)

visph

By quickly google search (deeply answering here to ALL of this questions cannot be done ^^), but with minimal selection and quite knowledge about:

1.Explain event delegation

https://davidwalsh.name/event-delegate

2.Explain how this works in JavaScript

https://github.com/getify/You-Dont-Know-JS/blob/master/this%20%26%20object%20prototypes/README.md

3.Explain how prototypal inheritance works

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Inheritance_and_the_prototype_chain

4.What do you think of AMD vs CommonJS?

https://stackoverflow.com/questions/16521471/relation-between-commonjs-amd-and-requirejs

5.Explain why the following doesn't work as an IIFE:
function foo(){ }();

open SL code playground on web browser (not on app'), type the question code "function foo(){ }();", and click on the yellow exclamation mark triangle icon in the left margin (or type the keyboard shortcut ALT+E after positioning the cursor on the corresponding line) will get you the TL;DR answer, gracefully to jslint (and do some search by your own to dive deeply on that subject

6.What needs to be changed to properly make it an IIFE?

answer is given by the jslint tip-info: "Function declarations are not invocable. Wrap the whole function invocation in parentheses"... it should be (function foo(){ })(); to work correctly as an IIFE...

7.What's the difference between a variable that is: null, undefined or undeclared?

http://lucybain.com/blog/2014/null-undefined-undeclared/

(and check also the "You don't know JS" -- YDKJS -- serie's book already linked above (about "this") wich is very informative on such subject)

8.How would you go about checking for any of these states?

... YDKJS give you the answer

9.What is a closure, and how/why would you use one?

still and always YDKJS, but also MDN (Mozilla Developer Network) already linked previously (about inheritance) is a really wide web good ressource:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Closures

10.Can you describe the main difference between a forEach loop and a .map() loop and why you would pick one versus the other?

MDN again...

https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Array/forEach

and

https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Array/map

...

But quickly, forEach() iterate over an array without modifying it (as long as you don't explicitly do so), while map() use returned value from the callback provided to change each value of the array on wich the method is called ;)

11.What's a typical use case for anonymous functions?

https://medium.com/@rlynjb/js-interview-question-what-s-a-typical-use-case-for-anonymous-functions-54cf547b2a0e

12.How do you organize your code? (module pattern, classical inheritance?)

That's a pretty personal question... wich don't get a unique and general answer ^^ At my point a view, a good skilled programmer is able to organize his code in the way its context crew would do ;)

13.What's the difference between host objects and native objects?

Native are built-in language objects (defined by the ECMAScript specification, such as String, Number, Array and so on), while hosted are those wich are deliver by specific implementation contexts of this parent specifications (ECMAScript not only have JS as child, but other languages/plateform, such as ActionScript -- script language for Flash technology, or JS implemented as server side language such as NodeJS): each provide some specific objects not necessarly available on others... JS is typically user-sided web/html language, and browsers provide "hosted" objects such as DOM implementation, and 'window', 'document' root global objects or 'console' (specific to each browsers even if they share some capacities, wich are not part of ECMAScript, but of W3C consortium or browser vendors...

http://thewebstop.blogspot.com/2017/01/host-objects-and-native-objects.html

14.Difference between: function Person(){} , var person = Person() , and var person = new Person() ?

check YDKJS for this subject (or do some search by yourself on internet): that's is highly related to the 'this' subject mentionned in the 2nd question above ^^

15.What's the difference between .call and .apply ?

Quickly, they are very similar, but one got arguments as in classical function call form, while the other got them at once argument array

http://hangar.runway7.net/javascript/difference-call-apply

16.Explain Function.prototype.bind

Again highly related to the understanding of the subject/topic of 'this': check a new time the YDKJS, or even the MDN ressources...

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

17.What's the difference between feature detection, feature inference, and using the UA string?

https://medium.com/@rlynjb/js-interview-question-what-s-the-difference-between-feature-detection-feature-inference-and-76d2e4956a9b

http://lucybain.com/blog/2014/feature-detection-vs-inference/

https://stackoverflow.com/questions/20104930/whats-the-difference-between-feature-detection-feature-inference-and-using-th"

18.Explain Ajax in as much detail as possible

https://developer.mozilla.org/en-US/docs/Web/Guide/AJAX

19.What are the advantages and disadvantages of using Ajax?

Topic ver subject to personnal tastes / point of views again... check google to get your own:

http://www.pritambaldota.com/what-is-ajax/

https://www.c-sharpcorner.com/interview-question/what-are-the-advantages-and-disadvantage-of-ajax

https://way2tutorial.com/ajax/ajax_advantages_disadvantages.php

20.Explain how JSONP works (and how it's not really Ajax)

https://en.m.wikipedia.org/wiki/JSONP

21.Have you ever used JavaScript templating?

... It could refer to different subjects:

• templating engine/frameworks

https://en.m.wikipedia.org/wiki/JavaScript_templating

https://www.sitepoint.com/overview-javascript-templating-engines/

• ES6 template litteral

https://css-tricks.com/template-literals/

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

22.If so, what libraries have you used?

According to this last question, it would probably most refer to the first one (engine/framework/libraries)... and this last question is about everyone's experience: I cannot provide link nor general answer, all the most as I personnaly don't much like framework/libraries and prefer generally improve my knowledge by coding from scratch and develop my own tools ^^ (with the think that when you deep master a language without helpers, you'll be more able to quickly learn any of them in futur if needed ;))