> For the complete documentation index, see [llms.txt](https://sandeepamaranath.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://sandeepamaranath.gitbook.io/notes/interview/technical/i-should-know-them.md).

# I must know them BEFORE INTERVIEW

Know these in and out

## For a FRONT-END ENGINEER position

1. What is JavaScript 
2. JS compile scenario
3. Datatypes of JS
4. What is the difference between querySelectorAll and getElementsByClassName (or getElementsByTagName)?  <https://chat.openai.com/share/bfc44d15-f3cb-45e4-b9ca-2216d79d52c0>
5. Debouncing and Throttling - Implementation of both, examples of each
6. Promises
7. Cookies, Local Storage, Session storage
8. Async Await
9. Var, Let, and Const
10. Iterator and Iterable
11. Generator
12. Call, Bind, and Apply
13. Closures - Advantages, Disadvantages, with an example implementation
14. Map vs Set for **problem-solving**
15. Array and Object iteration method **problem-solving**
16. Js Working behind the scenes
17. Event loop
18. Function types
19. Ways to create an object
20. Prototypal inheritance
21. this keyword
22. \== vs ===
23. Type coercion
24. Hoisting
25. nan vs undefined vs not-defined
26. Pass by value vs reference
27. Currying - Methods of creating currying
28. DOM
29. TDZ
30. Map, Reduce, and Filter

## Must watch videos

### **Top 5 JS interview questions**

{% embed url="<https://www.youtube.com/watch?v=6Wzj7kxfRdI&ab_channel=JoshuaFluke>" %}

### Tricky JS interview questions

{% embed url="<https://www.youtube.com/watch?v=jh86NGG9jdE&ab_channel=freeCodeCamp.org>" %}

### Javascript coding challenges practice

{% embed url="<https://www.youtube.com/watch?v=M2bJBuaOeOQ&ab_channel=TraversyMedia>" %}

### My JS notes, and CSS

* For JS theory, study the JS notes on gitbook, and for promises, study my handwritten notes or refer to code with harry videos quickly
* For CSS, study W3 schools and know these concepts
  * How to select CSS children
  * If green div is inside blue div, if blue div is hovered then green div should disappear
  * If green div is hovered, blue div can't disappear as it is the parent so you need JS. See how to do it in JS&#x20;
  * For these things you need to study CSS Selectors -  <https://www.w3schools.com/css/css_selectors.asp>

### Accordion&#x20;

* Do the accordion app in Plain HTML, JS and also do this in react
* That way, it is a good practice of JS and React before you go to interview

### Application Form

* Do a small HTML, JS app where you have 3 inputs, username, email and phone. If they are empty then you should show an error message that is already written in HTML (just apply css class in js to show the error). Once the form is good, submit it so that it should be added to an array (window object maybe) and could be shown on the screen.
* Do the same in react

### Image slider

* Do an image slider in JS
* Do it in react as well

## For a BACKEND ENGINEER position

&#x20;You should practice these before you go to interview

### SQL

* Practice SQL from <https://www.sql-practice.com/>. There are around 42 questions here including Easy, Medium and Hard.
* Solve Leetcode top 50 questions of SQL, <https://leetcode.com/studyplan/top-sql-50/>

### DSA

* Practice DSA from my notion notes