What is the required level of knowledge for a junior React.js Developer?

Question

JavaScript

I have an interview on the nose, and I would like to test my knowledge before it, and consolidate what may not be completely clear. In your opinion, what should a junior React developer know and be able to do, not including the basics of js, within the React-Redux application itself, and what subtleties are most important to understand, you can provide examples, or some kind of list, I will be very grateful.

Answer 1

UPDATE: real test cases and breakdowns here , answers to all questions from a post on my blog about learning react .
Sorry, but the standard task, about "write an add function that, when called add(1)(2), will return 3" - put many on the shoulder blades =) So get ready ..
0) What problem does react solve?
1) Does setState fire immediately? If not, then how to execute code that will be 100% executed after the new state is set?
2) Why do many people constantly write in constructor: this.FUNCTION_NAME = this.FUNCTION_NAME.bind(this) and hence the question is what is equal to this in different places of your component...
3) in which lifecycle methods should xhr requests be executed? In what is it worth "updating state based on props"?
4) What happens if you call this.setState in the component's render method?
5) why componenWIllUnmount is needed, give an example ..
6) Controlled, not controlled components
7) How to organize routing in React application? (answer: take react-router - it's fine, but it would be cool if you could tell how it works approximately) *
8) Why do we need propTypes? What happens to them in a production build?
9) How can you conveniently "debug" someone else's application code written in react (a hint towards React devtools)
...
0) What problem does redux solve?
1) Why do many create NAME_REQUEST / NAME_SUCCESS action types? And at the same time, what is an "action" and what is an "action creator" ...
2) What is a reducer? Can you write a simple reducer without react/redux?*
3) What is redux-thunk for? How does he work? Write (you can pseudo-code) an asynchronous action creator (or, if you are tired of talking in "terms" - asynchronous aciton)
4) How do application components get "props" from the "store"? *
5) Is it possible (and is it considered normal) to use state, if using Redux?
6) Why do we return new objects in reducer'ax? Give an example when you return a new object, and when you return the same one.
6.5) And also, "how does it work in js?". For example:

let obj1 { name: 'Test', age: 100 }
let obj2 = obj1
obj2.name = 'Test_new'

What will be in obj1, why? When can objects be equal?
7) What does the connect function (from react-redux) return?
...
General :
0) package.json
1) Webpack, gulp, etc...
2) node.js
3) promise
Something practical :
1) How would you validate a form if validation errors come after submit'a it on the server..
2) Why the following code doesn't work , make it work
...
I don't pretend to be the truth, but such questions took place in interviews. In a conversation, you can find out a lot with additional questions and so on. Also, if some of the questions are unknown to you - it does not matter, many cannot even answer half of them.
ps Perhaps I will add ...
pps marked with an asterisk, in my opinion, not the most necessary questions for a junior interview.

Answer 2

Junior React developer?
I think it sounds kind of weird.
It is important to understand the basic foundations of the functional paradigm, its difference from OOP, understanding the flux architecture and data flows, a confident level of JS (ES6), how asynchrony works, all sorts of ajax-api (axious, fetch), state machine (what is it and why is it needed). About html \ layout, of course.
When I got into React without a good JS skill, I didn’t understand what was happening around.

Answer 3

I myself would not mind asking this about Angular2, but apparently I know a little secret - read vacancies, and see what is relevant to know today for Junior React Developer.
Speaking specifically about React, the more the better. Though abstract, but accurate.

Answer 4

in almost every interview there is such a thing as "write a polyfill for bind", so you need to understand how "this" works in JS.
plus, React / Redux is based on functionality, so you can expect questions about HOC (for example, connect in react-redux), map-reduce, etc.
you also need to know how life cycles work in React, well, for example .. if in shouldComponentUpdate return false, will componentWillReceiveProps be called?
Well, for sure you need to know about the mechanism of work of promises, IMHO.