JS Essentials

Question 1

Are variables uppercase or lowercase

Answer 1

Start with lowercase, then use camelcase

Question 2

Are objects and constants uppercase or lowercase

Answer 2

Objects and classes start with uppercase, constants are all caps

Question 3

what do you end each statement with

Answer 3

a semicolon

Question 4

how do you set a variable as a string

Answer 4

var sting=”string full of words”

Question 5

How do you deal with quotation marks in a string when declaring a variable

Answer 5

Escape the quotes
var escQuote = "quotes can be \"escaped\"."

Question 6

how do you find the data type of a variable

Answer 6

console.log(typeof variableName);

Question 7

what are the data types of variables

Answer 7

numeric, string, bollean, null, undefined, symbol

Question 8

Math:
how do you increment a variable by 1?
subtract by 1?

Answer 8

var a;
a++;

or
a–;

Question 9

Math:
var a=1;
what are the results of the following:
console.log (a);
console.log (++a);
console.log (a++);

Answer 9

console. log (a); produces 1
console. log (++a); produces 2
console. log (a++);

Question 10

var a = 4;
var b = "5";
var sum = a + b;
console.log (sum);

Answer 10

45

because 5 is a string it assumes you are combining strings

Question 11

var a = 4;
var b = "5";
var subt = a-b; 
var mult = a*b; 
var div = a/b;

Answer 11

console.log (subt); -1
console.log (mult); 20
console.log (div); .8
because you are not using + it assumes 5 is a number

Question 12

var a = 5;
var b = '5';
var theNumbersMatch;

if ( a ==b ){
	theNumbersMatch = true;
	} else {
	theNumbersMatch =  false;
	}
console.log ("the numbers match: " + theNumbersMatch);

Answer 12

True because the string of 5 is 5

Question 13

How do you write
if a equals b and c equals d
if a equals b or c equals d
if a equals b xor c equals d

Answer 13

if (a == b && c == d) {}
if ( a == b || c== d) {}
if (( a == b || c == d) && (( a == b) ! = (c ==d)) {}

//AND - both a and b are true
//OR - either a or b are true or BOTH
//xor if a equals b xor c equals d (not both)

Question 14

rewrite the following as a ternary operator
if ( a==b){
	console.log("match");
 } else {
	console.log ("no match");
	}

Answer 14

a == b ? console.log (“match”) : console.log(“no mactch”);

Question 15

var pens = [“red”, “blue”, “green”, “orange”];

how do you find the orange based upon its position?
how do you change the value in the array by referring to its position?

Answer 15

var fourthPen = pens[3];
console.log (fourthPen);

pens [3] = “purple”;

Question 16

var pens = [“red”, “blue”, “green”, “orange”];

how do you find the length of the array?

Answer 16

console.log (“array length:”, pens.length);

Question 17

var pens = [“red”, “blue”, “green”, “orange”];

How do you reverse the array?

Answer 17

console.log(pens.reverse());

Question 18

var pens = [“red”, “blue”, “green”, “orange”];

how do you return the first value of the array?

Answer 18

console.log (pens.shift());

Question 19

var pens = [“red”, “blue”, “green”, “orange”];

how do you add values to the front of the array

Answer 19

pens.unshift(“purple”, “black”);

Question 20

var pens = [“red”, “blue”, “green”, “orange”];

how do you remove the last value of the array

Answer 20

console.log (pens.pop());

Question 21

var pens = [“red”, “blue”, “green”, “orange”];

how do you add values to the end of the array

Answer 21

pens.push (“pink”, “prussian blue”);

Question 22

var pens = [“red”, “blue”, “green”, “orange”];

How do you take blue away from the array?

Answer 22

pens.splice (1,1);

Question 23

var pens = [“red”, “blue”, “green”, “orange”];

how do you make a copy of an array?

Answer 23

var newPens = pens.slice();

Question 24

var pens = [“red”, “blue”, “green”, “orange”];

how do you return the values of the array in a comma separated list?

Answer 24

var arrayString = pens.join(separator);
console.log('string from array: ', arrayString);

Question 25

what are the three types of functions and when do they execute

Answer 25

named - when called anonymous - run once they are triggered by an event immediately invoked - when the browser encounters them

Question 26

What is variable scope?

Answer 26

Where the variable will be used. Either global or local. Global - you can access it anywhere in the script. If you change it in a function it is changed globally. Local - if you declare a variable in a function then it is local to that function and cannot be used outside of it.

Question 27

what is the scope of a let statement

Answer 27

let is a block scope variable - it can only be used in that statement

Question 28

Are objects written as lowercase, uppercase or camelcase?

Answer 28

Objects are capitalized

Question 29

what are the three types of functions

Answer 29

named, anonymous, immediately invoked

Question 30

what are the 4 ways to invoke a function

Answer 30

1. as a function 2. as methods 3. constructors 4. call and apply methods

Question 31

when does an immediately invoked expression happen

Answer 31

when the browser encounters them

Question 32

what is a constant

Answer 32

can't be changed once defined

Question 33

what is a let

Answer 33

a block scope variable, only available in that function

Question 34

are objects capitalized or lower case

Answer 34

capitalized

Question 35

``` var a = 4; var b = "5"; var sum = a + b; ```

Answer 35

produces 45 because javascript assumes you want a string since 5 is a string

Question 36

``` ar a = 4; var b = "5"; var subt = a-b; var mult = a*b; var div = a/b; ```

Answer 36

``` var subt = a-b; //will produce 1 var mult = a*b; //20 var div = a/b; //.8 ```

Question 37

what is the difference between: = == ===

Answer 37

= is assignment == equal === strictly equal

Question 38

``` var a = 5; var b = '5'; var theNumbersMatch; ``` ``` if ( a ==b ){ theNumbersMatch = true; } else { theNumbersMatch = false; } would produce what? ```

Answer 38

true, because the string of 5 is 5

Question 39

``` var a = 5; var b = '5'; var theNumbersMatch; ``` ``` if ( a === b ){ theNumbersMatch = true; } else { theNumbersMatch = false; } would produce what? ```

Answer 39

false

Question 40

``` //boolean if (a ==true) {} what is the shorthand ```

Answer 40

if (a) {}

Question 41

write: | if a equals b and c equals d

Answer 41

if (a == b && c == d) {}

Question 42

write: | if a equals b or c equals d

Answer 42

if ( a == b || c== d) {}

Question 43

write | if a equals b or c equals d OR BOTH

Answer 43

if ( a == b || c== d) {}

Question 44

``` write this as a ternary operator if ( a==b){ console.log("match"); } else { console.log ("no match"); } ```

Answer 44

a == b ? console.log ("match") : console.log("no mactch");

Question 45

var pens; pens = new Array ["red", "blue", "green", "orange"]; find the fourth value in the array

Answer 45

``` var fourthPen = pens[3]; console.log (fourthPen); ```

Question 46

var pens; pens = new Array ["red", "blue", "green", "orange"]; Change the fourth value in the array to purple

Answer 46

pens [3] = "purple";

Question 47

var pens; pens = ["red", "blue", "green", "orange"]; find how many elements are in the array

Answer 47

console.log ("array length:", pens.Length); //returns 4

Question 48

var pens; pens = ["red", "blue", "green", "orange"]; how to you reverse the array? remove the first value of the array? remove the last value? find a specific position and remove it?

Answer 48

there are many standard methods to manipulate arrays pens. reverse(); pens. shift() pens. pop() pens. splice (pos, n)

Question 49

var pens; pens = ["red", "blue", "green", "orange"]; how do you create a copy of an array and assign it to a new variable

Answer 49

use the slice method ``` var newPens = pens.slice(); console.log("new pens:", newPens); ```

Question 50

What is hoisting?

Answer 50

javascript moves all declarations to the top if you declare anything at the bottom but run it at the top it will work. the only time it won't work is if you declare it at the bottom and assign a value, but then call it at the top, it will be undefined.

Question 51

how would you run this? ``` var a = 5/7; var b = 18/25; ``` ``` var theBiggest = function(){ var result; a>b ? result = ["a",a] : result = ["b", b]; console.log(result); } ```

Answer 51

theBiggest(); or to get it to display: console.log(theBiggest());

Question 52

What is the difference between global and local scope

Answer 52

global - in the root you can access anywhere in the script if you make a change to it inside a fuction then it is changed globally if you declare var in a funtion then it is local and cannot be used ouside of that function

Question 53

what is the difference between constant and let

Answer 53

constant can't be changed once defined | let is a block scope variable - smaller scope

Question 54

are objects lowercase, capitalized or camelcase?

Answer 54

capitalized

Question 55

how do you define an object and its properties?

Answer 55

var course = new Object(); //then define the properties of the object course. title = "java training"; course. instructor = "joe smith"; course. level = 1; course. published = true; ``` //or shorthand var course = new Object(); var course = { title: "java training", instructor: "heather morris", level: 1, published: true, } ```