basic

Question 1

what is mostly use const or let?

Answer 1

const.

Question 2

when should you use let?

Answer 2

when the value is going to change

Question 3

playground to practice js?

Answer 3

jsbin.com

Question 4

how do you write a normal js function ?

Answer 4

function myFunc() {
}

Question 5

assing an arrow function to a variable?

Answer 5

const myFunc = () => {
}

Question 6

what can you do with const process = (name) => {
}?

Answer 6

remove parenthesis in the single argument

Question 7

when you decalre a function in js do you have to declare the argument type?

Answer 7

no.

Question 8

if your arrow function does not take arguments can you go const work = => {} ?

Answer 8

no you have to use const work = () => {}

Question 9

if the body of your arrow function only has a return statement what can you do?

Answer 9

remove the {}. e,g,, const multiply (number) => number * 2;
even better const multiply number => number * 2;

Question 10

what are default exports? and imports

Answer 10

when you export an object in your .js by saying at the end export default person
This makes the import for only the default, i.e.,
import prsn from ‘./person.js’

Question 11

what are name imports? and exports

Answer 11

name exports:
export const clean = () => {...}
export const baseData = 10; 
   notice there's no default keyword.
the import has to go like:
import {baseData } from './utility.js' or
import {baseData, clean} from './utility'

Question 12

others syntax’s allowed for import?

Answer 12

import {smth as Smth} from ‘./utility.js’

import * as bundled from ‘./utility.js’

Question 13

create a class called Person in js

Answer 13

class Person {
      constructor() {
            this.name = 'Max';
     }

 printName() {
        console.log(this.name); 
} }

Question 14

instanciate class Person and call method printName

Answer 14

const p = new Person();
p.printName();

Question 15

create a class Human and make Person inherit from it

Answer 15

class Human {
       constructor() {
             this.gender = 'M';
       printGender() {
            console.log(this.gender); 
       }
}

class Person extends Human {
       constructor() {
            super(); 
            this.name = 'Max';
       }
      printName() {
            console.log(this.Name);  
      }
}

Question 16

what does ES6 means?

Answer 16

ECMA Script 6 (European Computer Manufacturers Association)

Question 17

what is the official name of JavaScript?

Answer 17

ECMA Script

Question 18

what is Babel?

Answer 18

is a transpiler, that does not compile but translate from one language to other. Babel translate from ES6 to normal Javascript

Question 19

Es6 way to declare a class

Answer 19

class Person extends Human {
        name = 'Max'; 

    printName  = () => { 
           console.log(this.name); 
    } }

Question 20

spread operator, how does it work?

Answer 20

const newArr = [ ... oldArr, 1, 2]; 
const newObj = { ... oldObj, newProp : 5 }

Question 21

rest operator, how does it work? (pending)

Answer 21

const argSorter = (… args) => return args.sort();

Question 22

what is the output difference between :
const numbers = [1, 2, 3]; 
const newNumsA = [...numbers, 4];
and
const newNumsB = [numbers, 4];

Answer 22

A gives [1, 2, 3, 4]

B gives [ [1, 2, 3], 4]

Question 23

how do you create an object literal?

Answer 23

var person = {firstName:”John”, lastName:”Doe”, age:50, eyeColor:”blue”};

Question 24

what does === means?

Answer 24

equality that checks for value and type

Question 25

what is an array destruction? for example array [1, 2, 3] destroyed to the first two elements. (pending)

Answer 25

const numbers = [1, 2, 3]; 
[a, b] = numbers; 

then you can use a as a var with value = 1 and b = 2
also you can do [a, , c] = numbers then c = 3

Question 26

and what is object destructing?

Answer 26

same. e., g. const person = { name: 'Daniel', age: '8' ];
{name} = person; 
now name has 'Daniel'

Question 27

value types in js

Answer 27

numbers, booleans and strings!

Question 28

reference types in js?

Answer 28

arrays and objects

Question 29

what is a superused way to use the spread operator?

expand

Answer 29

to copy reference types as value types, i.e., actual assigning a new pointer to the copy

Question 30

array map function example

Answer 30

you get an array: const numbers = [1, 2,3]; 
then you say: 
numbersCopy = numbers.map( n => n * 2);

Question 31

is an array map function a reference or a value copy?

Answer 31

a value copy

Question 32

array function for filter,

Answer 32

arr.filter(c => c === 4);

Question 33

what does a LTS version mean?

Answer 33

Long Term Support

Question 34

how do you install environment to work on react?

Answer 34

npm intsall create-react-app -g

Question 35

what is the name of the package for the build workflow?

Answer 35

create-react-app

Question 36

what are the 3 dependencies added to a react project?

Answer 36

react, react-dom and react-scripts

Question 37

what is the main html file of a react app?

Answer 37

index.html

Question 38

what does the main html mainly contains?

Answer 38

a <div></div> which is where all the react magic will happen

Question 39

how do you cover that javascript is not enabled, i.e., how do you tell the user to enable it?

Answer 39

You need to enable JavaScript to run this app.

Question 40

what is manifest.json connected with?

Answer 40

progressive development of the application

Question 41

what are the 4 scripts available in the build workflow?

Answer 41

start, test, build, eject, i.e., npm start, npm test, npm run build, npm run eject don’t use eject

Question 42

what is the most important, i.e., entry point for a react app?

Answer 42

index.js. it has all the imports and it calls reactDOM.render() method.

Question 43

how do you get the root element from the dom?

Answer 43

document.getElementById(‘root’)

Question 44

get a random number (bet 0 and 1)?

Answer 44

Math.random()

Question 45

get the integer part of a number?

Answer 45

Math.floor()