JavaScript

Question 1

javascript vs java

Answer 1

• js is interpreted, java is compiled
• similar syntax
• js is more relaxed

Question 2

data types

Answer 2

Primitive:
- number (99, 0.8, -1)
- string (“hello”)
- boolean (true or false)
Complex:
- undefined (var x;)
- Objects (special)
- function (user-defined)

objects are special data types that have functions and data associations

Question 3

javascript arithmetic

Answer 3

• a + b
• a - b
• a / b
• a * b
• a**b (exponential)
• a % b (modulus)

Question 4

javascript arithmetic shortcuts

Answer 4

• a++ and a– to add or subtract 1 from a number variable
• a+= b is a = a+ b (and same for -,/,*,%)

Question 5

javascript arithmetic precedence

Answer 5

BEDMAS

brackets, exponents, division/multiplication, addition/subtraction

Question 6

== and ===

Answer 6

equivalency and strict equivalency; check to see if the value is the same and check to see if the value AND data type are the same

ex. string “5” compared to number 5 is true for == and false for ===

Question 7

Javascript comparison operators

Answer 7

• == (equal to)
• === (equal to and equal type)
• != (not equal to)
• !== (not equal to or not equal type )
• > (greater than)
• < (less than)
• > = (greater than or equal to)
• <= (less than or equal to)

Question 8

number to string conversion trick

Answer 8

numberVar = numberVar + “”

concatenation of a number and string type creates a string

Question 9

control statements

Answer 9

• if/else if/else
• while/do-while loops
• for loops

Question 10

function syntax

Answer 10

functionName(param1,param2..etc) {
function code
}

Question 11

deterministic vs nondeterministic loops

Answer 11

for vs while

Question 12

var vs let vs const

Answer 12

var is function scope let and const is block scope

Question 13

string concatenations

Answer 13

“hello” + “world” = “helloworld”
“hello” + “ “ + “world” = “hello world”
“hello” + 123 = “hello123”
123 + “” = “123”

Question 14

Style Guide

Answer 14

• camelCase for identifiers
• avoid $
• identifiers start with _ or letters

Question 15

JS Events

Answer 15

Things like clicks, entering text, etc.

Question 16

event handler

Answer 16

function onClick () {
}

Question 16

html elements associated with events

Answer 16

<button>
<input></input></button>

<textarea>
</textarea>

Question 16

DOM

Answer 16

Every element (tag) in an HTML page is an object that can be accessed in JS through the document object via dot notation

Question 17

addEventListener and removeEventListener

Answer 17

takes two parameters, event name and function name

Question 17

dot notation

Answer 17

Each element’s properties and methods can be accessed using dot notation:

element.style.color = white;

Question 17

DOM examples

Answer 17

const element = document.querySelector(‘img’);
element.src = ‘newImg.png’;
element.style.background.color = ‘blue’;

Question 18

changing an element’s class

Answer 18

the classes used in css can be added or removed using:

.classList.add(‘className’);
.classList.remove(‘className’);

Question 19

event objects

Answer 19

implicitly passed to the handler methods of the function:

function onClick(event) {
const clickSrc = event.currentTarget
}

Question 20

other DOM properties

Answer 20

element.id
element.value
element.innerHTML (unsecure)
element.textContent

Question 21

DOM element creation/removal

Answer 21

let element = document.createElement(tag);
element.appendChild(anotherElement);
element.remove(anotherElement);

Question 22

recursion

Answer 22

-never more efficient as it’s iterative counterpart
-used when the problem itself is recursive by nature (merge/quick sort, tree traversal, balanced strings, etc)

Question 23

stack frame (activation record)

Answer 23

contains all info necessary for tracing a function call; parameters, local vars, return addresses, etc

when a function is called it’s stack frame is created, initialized, and pushed on to the stack

when a function is finished its stack frame is popped off the stack