Javascript

Question 1

What Data Types does Javascript use?

Answer 1

boolean
undefined
string
symbol
object
null
number

Question 2

Declare a variable “cats”

Answer 2

var cats;

variables cannot start with a number or contain spaces.

Question 3

Which way does assignment go

Answer 3

right to left.

For example. Below, myVar gets defined as 5 and then myNum gets defined as myVar (which is currently 5).

myVar = 5;
myNum = myVar;

Question 4

what does NaN mean

Answer 4

Not a Number

happens when you use an undefined variable in an equation.

Question 5

what does i++ operator do?

Answer 5

same thing as typing i=i+1

Question 6

what does i– operator do?

Answer 6

same thing as typing i=1-1

Question 7

What does the % operator do?

Answer 7

remainder

gives you the remainder of the numbers you are dividing.

4 % 3 = 1

used as a way of testing even and odd numbers. If you remainder anything by 2 it is even if the remainder is 0 and odd if the remainder is 1.

Question 8

+= operator

Answer 8

does the assignment and addition in one step.

MyVar += 5 means that MyVar is 5 and that you should add 5 to it? I don’t entirely understand how this one works.

Question 9

\n

Answer 9

new line

Question 10

\r

Answer 10

carriage return (what is this?)

Question 11

what is a carriage return

Answer 11

(figure it out)

Question 12

\t

Answer 12

tab

Question 13

\b

Answer 13

backspace

Question 14

\f

Answer 14

form feed

Question 15

What do you call it when a + operator is used with a string value

Answer 15

concatenation

Example:

var myStr =”This is the start.”+ “ This is the end.”

Output is: “This is the start. This is the end.

Question 16

How do you count the number of characters in a string such as the following variable.

Then assign that length to another variable

var catName = “steve”

Answer 16

catNumber = catName.length;

The number would be 5 since that’s how many letters are in “steve.” So now catNumber would equal 5

Question 17

Use bracket notation to assign the first letter of a last name as a variable to var firstLetterOfLastName.

Answer 17

var firstLetterOfLastName = "";
var lastName = "Lovelace";

firstLetterOfLastName = lastName[0];

Question 18

in javascript, strings are “immutable” which means what?

Answer 18

Once a string is created it cannot be altered once created

Question 19

What is the output of the following?

var name = "bob";
var letter = name[2];

Answer 19

b

Question 20

What is the output of:

var catName = "Jerry";
var letter = catName[catName.length - 4];

Answer 20

e

Question 21

What is the output of:

var lastName = “Marks”;

var letter = lastName [lastName.length - 2];

Answer 21

k

Question 22

What is an array

Answer 22

It is a type of variable that can store multiple pieces of information.

var array = [“kitty”, 45]

Question 23

What is this?

var ourArray = [[“the universe”, 42], [“everything”, 101010]];

Answer 23

It is an array nestled into two arrays.

Question 24

challenge: Type the following in under 20 seconds.

4 tries = good
3 tries = great
1st try = perfect

var myArray = [[“cats”, 43], [“dogs”, 35]];

Answer 24

.

Question 25

how do you access the data inside an array?

Answer 25

by using an index

var myArray = ["pigeons","cats","turtles"];
var myData = myArray[0];

Output = “pigeons”

Question 26

What is the output of

var catScores = ["turtles", 44];
var pigeonScore=catScores[1];

Answer 26

var pigeonScore=44

an index of 0 would create an output of “turtles” instead of 44

Question 27

Add 4 to the end of the array

var myArray = [3,2,1]

Answer 27

myArray.push(4);

myArray now = [3, 2, 1, 4];

myArray.push([4,3])

myArray = (3,2,1,[4,3])

Question 28

What is a function?

Answer 28

a reusable piece of code.

example:

function ourReusableFunction() {
  console.log("Kiss puppies");
}

ourReusableFunction();

output is “Kiss puppies”

Question 29

Review this exercise

Answer 29

https://www.freecodecamp.com/challenges/passing-values-to-functions-with-arguments

Question 30

Which type of variable of the same name takes precedent?

Global or local?

Answer 30

Local

https://www.freecodecamp.com/challenges/global-vs-local-scope-in-functions

Question 31

what is a local variable

Answer 31

it is only visible within the function

Question 32

How do you pass values into a function?

Answer 32

Arguments

https://www.freecodecamp.com/challenges/return-a-value-from-a-function-with-return

Question 33

How do you send values back out of a function?

Answer 33

return statements

function plusThree(num) {
  return num + 3;
}
var answer = plusThree(5); // 8

https://www.freecodecamp.com/challenges/return-a-value-from-a-function-with-return

Question 34

Create a function that allows you to multiply a number by 8

Answer 34

function timesFive(num) {
  return num * 8;
}

var answer = timesFive(3);

// 24

Question 35

What are parameters?

Answer 35

Variables that act as placeholders for the values that will be input into a function.

Example (a and b are the parameters for functionWithArgs() the function has the console log a + b. bellow there is a call for the function defining the parameters as a=”cat,” and b = 4.

The function would then log cat,4.

function functionWithArgs(a,b) {
  console.log(a+b);
}

functionWithArgs(“cat,”,4);

Question 36

What do you call values that are “passed” into a function when it is called?

Answer 36

Arguments

Question 37

How do you add a new value to the end of an array?

Answer 37

arrayName.push(x)

Question 38

How do you add a new value to the beginning of an array?

Answer 38

arrayName.unshift(x)

Question 39

How do you take away a value from the beginning of an array?

Answer 39

arrayName.shift

Question 40

How do you take away a value from the end of an array?

Answer 40

arrayName.pop

Question 41

What are boolean’s values?

Answer 41

True or False

Question 42

what does “if” do?

Answer 42

It triggers code to execute inside { } if certain conditions are true or false as defined by conditions in the braces ( )

https://www.freecodecamp.com/challenges/use-conditional-logic-with-if-statements

Question 43

Can an “==” compare two types of data? (Strings and numbers?)

Answer 43

Yes. It has to convert them first, but then can compare them and declare true or false.

1 == 1 // true
1 == 2 // false
1 == ‘1’ // true
“3” == 3 // true

****Strict Equality on the other hand === does not convert strings to numbers so the following:

1 === 1 // true
1 === 2 // false
1 === ‘1’ // false
“3” === 3 // false

Question 44

!=

Answer 44

inequality operator. “Not Equal”

examples

1 != 1 // false
1 !=2 // true

Question 45

!==

Answer 45

Strict inequality.

will not convert data types

1 !== “1” // true
1 !== 1 // false

Question 46

& &

Answer 46

“logical and” operator

You can nest if statements

function inThePocket (val) {

if (val > 3 &amp;&amp; val < 15) { 
     return "in the pocket"
     }
   return "outside the parameters"
}

(Free code camp: comparisons with logical and operator)

Question 47

||

Answer 47

“logical or operator” returns true if either of the operands is true. Otherwise it returns false.

function testLogicalOr(val) {
  // Only change code below this line

  if (val < 10 || val > 20) {
    return "Outside";
  }
  // Only change code above this line
  return "Inside";
}

return testLogicalOr(15) // inside
return testLogicalOr(9) // outside

Question 48

How do you chain multiple if statements together

Answer 48

by using “else/if”

Function(x){
if (x < 5) { return y };
else if (x > 5) {return z};
else {return q};
}