JS - Udemy

Question 1

ES6 def & features

Answer 1

Var, arrow functions?

Question 2

How to get to & run code in console?

Answer 2

• Control+Shift+C or Inspect or More Tools; -

Question 3

What is modulo? + ex

Answer 3

• %, returns remainder; - 25 % 5 = 0

Question 4

How to notate exponents?

Answer 4

5**2 returns 25

Question 5

What is the order of operations?

Answer 5

PEMDAS - parentheses, exponents, mult, div, add, sub

Question 6

What is NaN & what will return it?

Answer 6

0/0; NaN + a number;

Question 7

How does the browser read JS?

Answer 7

• HTML file, include

Question 8

Quick way to view .js in browser?

Answer 8

• Open html file in file explorer that contains .js tag

Question 9

What’s an Unary Operator? Ex.

Answer 9

• ++ (existingVar+=1); – (existingVar-=1);

Question 10

What are the primitive types?:

Answer 10

• Number, String, Boolean, Null, Undefined

Question 11

Booleans

Answer 11

• true & false; - 1 or 0

Question 12

What does null mean?

Answer 12

• Absence of any value

Question 13

What does Undefined mean?

Answer 13

• Variable with no assigned value

Question 14

List the falsey values

Answer 14

false, 0, “”, null, undefined, NaN

Question 15

How to get the index (content) of a string/letter? ex.

Answer 15

string[1] = t

Question 16

How to convert a string to upper? ex

Answer 16

string.toUpperCase( )

Question 17

How to convert a string to lower? ex

Answer 17

string.toLowerCase( )

Question 18

What does Trim do? ex.

Answer 18

” string “.trim = “string”

Question 19

How to get the index (letter) of a string? ex

Answer 19

string.indexOf(“tr”) = 1

Question 20

How to return a fragment of a string? ex

Answer 20

string.slice(0,2) = “str”

Question 21

How to substitute part of a string? ex

Answer 21

string.replace(‘g’, ‘z’) = “strinz”

Question 22

How to keep a quote or backslash in a string from fucking up your day? ex

Answer 22

• Escape Characters; - / preceding a “ or ‘ or /

Question 23

How to insert expressions, variables etc. into a string? ex

Answer 23

• Template Literals –NOT QUOTES! TILDE; - String ${3+4} ${var}

Question 24

What is the Math object? ex

Answer 24

• Math. contains methods

Question 25

What are a few Math objects?

Answer 25

• Math.round(4.9) = 5; .floor, .abs, .pow, .random

Question 26

What returns the data type?

Answer 26

typeof ___

Question 27

How to parse numbers from a larger string?

Answer 27

• parseInt; - parseFloat;

Question 28

What’s the difference between == and ===?

Answer 28

` === checks for equality AND type

Question 29

IF, ELSE IF, ELSE: EX: Write a function - if x is > 10 return “>10”, else if x > 6 return that, else returns < 6

Answer 29

"if (x > 10) { 
   console.log('>10');
}
else if (x < 10 &amp;&amp; x > 6) {
   console.log('>6');
}
else {
console.log('<6')
}"

Question 30

What is ! Ex

Answer 30

• Reverses truthiness; - !(3 < 4) = false

Question 31

What is the order of Logical Operators?

Answer 31

!, &&, then || (notwithstanding parentheses)

Question 32

EX: What conditional is best when you have one thing you’re checking against a set of values?

Answer 32

"switch (day) {
 case 1:
   return ""Monday"";
   break;
 case 2:
   return ""Tue"";
 default:
   return ""else value here"";
}

use break for each case you don’t want to stop - default is ““else”””

Question 33

What’s another way of writing an IF/ELSE statement?

Answer 33

”- Ternary Operator; -

num = 6

num === 7 ? console.log(““lucky!””) : console.log(““BAD!””); = BAD!”

Question 34

JS array format?

Answer 34

let or const arrName = [0,1,2,3]

Question 35

What are the 4 basic Array Methods?

Answer 35

• Push (add to end) , Pop (remove from end), Shift (remove from start), Unshift (add to start)

Question 36

How to join arrays?

Answer 36

old.concat(new)

Question 37

Arr method to search for a value?

Answer 37

arr.includes(‘string’)

Question 38

Arr method to reverse array?

Answer 38

arr.reverse()

Question 39

Arr method to combine elements?

Answer 39

arr.join(‘-‘)

Question 40

Arr method to copy portion of array?

Answer 40

arr.slice(start, end+1)

Question 41

Arr method to remove/replace elements?

Answer 41

arr.splice(startindex[deletecount[item1,item2,…

Question 42

Arr method to sort array?

Answer 42

arr.sort(compareFunction)

Question 43

What happens when you use const w/ arrays?

Answer 43

Elements can change, “Arr =” cannot be invoked

Question 44

What happens when you use const w/ arrays?

Answer 44

Elements can change, “Arr =” cannot be invoked

Question 45

EX: fitBitData obj

Answer 45

"const fitBitData = {
   totalSteps  : 588,
   totalMiles  :  2.3,
   avgSleep   :  '2:13'
};"

Question 46

How to access an Object Property?

Answer 46

obj[key] = value (key = number or ‘string’)

Question 47

EX: How to nest arr + obj in obj?

Answer 47

"const student = {
  name : 'Jon',
  strengths : ['Music','Art'],
  exams : {
    midterm : 92,
    final : 88
  }
};"

Question 48

EX: For Loop

Answer 48

“for(initial value[i]; condition; increment)

for(let i = 1; i <=10; i++){
  console.log('hello');
}"

Question 49

EX: How to loop over array? (Like each do | |?)

Answer 49

"for(let i = 0; i < array.length; i++) {
}"

Question 50

EX: While loop

Answer 50

“while(somethingIsTrue) {
action;
counter++;
}”

Question 51

EX: For..Of

Answer 51

”- Used for iterating through arrays

for (let ELEMENT of ARRAY) {
statement
}”

Question 52

For..In

Answer 52

”- Used for iterating through obj

for (let MOVIE in moviesObject) {
statement
}”

Question 53

JS ver. of Each_With_Index? ex.

Answer 53

“array.forEach(function (element, index) {

});”

Question 54

What to use instead of forEach when you want to stop looping upon solution? ex.

Answer 54

”- For loop with counter:

for (let i = 0; while i \_\_\_ condition; i +=1) {
}"

Question 55

How to create a hash table from arr? ex.

Answer 55

"let values = [4, 2, -1, 5, 6];
let hashTable = {};

values.forEach((value, index) => hashTable[value] = index);

hashTable[-1]; // 2
hashTable[6]; // 4
“

Question 56

What does the “break” keyword do in a loop?

Answer 56

• Stops loop in a while loop; - diff from switch?