JavaScript

Question 1

What is the purpose of variables?

Answer 1

helps store data to remember

Question 2

How do you declare a variable?

Answer 2

var declares/makes the variable

Question 3

How do you initialize (assign a value to) a variable?

Answer 3

you assign it with a = sign.

Question 4

What characters are allowed in variable names?

Answer 4

letters, $, underscore, and numbers(can be used as long as it’s not the first character)

Question 5

What does it mean to say that variable names are “case sensitive”?

Answer 5

if you accidentally capitalize a letter it is a WHOLE DIFFERENT VARIABLE.

Question 6

What is the purpose of a string?

Answer 6

it’s a way to hold a sequence of variables

Question 7

What is the purpose of a number?

Answer 7

to do math

Question 8

What is the purpose of a boolean?

Answer 8

a true or false statement

Question 9

What does the = operator mean in JavaScript?

Answer 9

an assignment

Question 10

How do you update the value of a variable?

Answer 10

no keyword is necessary (something = ‘something’)

Question 11

What is the difference between null and undefined?

Answer 11

null is a value that can only be assigned. undefined can come from many different things.

Question 12

Why is it a good habit to include “labels” when you log values to the browser console?

Answer 12

if you console.log without a label you don’t know what it really is.

Question 13

Give five examples of JavaScript primitives.

Answer 13

string, number, undefined, null, and boolean.

Question 14

What data type is returned by an arithmetic operation?

Answer 14

a number

Question 15

What is string concatenation?

Answer 15

adding strings together to make a bigger string

Question 16

What purpose(s) does the + plus operator serve in Javascript?

Answer 16

addition or concateanation.

Question 17

What data type is returned by comparing the two values (<, >, ===, etc)?

Answer 17

boolean

Question 18

What does the += “plus-equals” operator do?

Answer 18

adds the variable

Question 19

What are objects used for?

Answer 19

They group together a set of variables and functions.

Question 20

What are object properties?

Answer 20

variables that are apart of an object.

Question 21

Describe object literal notation.

Answer 21

{
something: value,
something2: value2,
}

Question 22

How do you remove a property from an object?

Answer 22

You use the keyword delete and then use dot notation to identify the property or method you want to get rid of.

Question 23

What are the two ways to get or update the value of a property?

Answer 23

var varName = object.property/method name
OR
object.propertyname = “property value”

Question 24

What are arrays used for?

Answer 24

good for rendering lists of data that are important or not important.

Question 25

Describe array literal notation.

Answer 25

variable followed by a name followed by bracket notation followed by strings, or a list of items.

Question 26

How are arrays different from "plain" objects?

Answer 26

Arrays are a special type of variable that is also mutable and can also be used to store a list of values.

Question 27

What number represents the first index of an array?

Answer 27

0

Question 28

What is the length property of an array?

Answer 28

it tells you how many properties you have in the array

Question 29

How do you calculate the last index of an array?

Answer 29

you subtract the length of the array by one and then assign it to a new variable.

Question 30

What is a function in Javascript?

Answer 30

a chunk of code that returns something.

Question 31

Describe the parts of a function definition.

Answer 31

1. function keyword. 2. optional name. 3. a list of parameters. 4. opening curly brace. 5. optional return. 6. closing curly brace.

Question 32

Describe the parts of a function call.

Question 33

When comparing them side-by-side, what are the differences between a function call and a function definition?

Question 34

What is the difference between a parameter and an argument?

Answer 34

putting things in the ()

Question 35

Why are function parameters useful?

Answer 35

They allow for the function to take in values. if they weren't there. functions would do the same thing over and over again.

Question 36

What two effects does a return statement have on the behavior of a function?

Answer 36

return spits out a value that the rest of the coed can use. Anything under the return statement WILL NOT RUN.

Question 37

Give 6 examples of comparison operators.

Answer 37

==, !=, ===, !==, >, >=, <, <=

Question 38

What data type do comparison expressions evaluate too?

Question 39

What is the purpose of an if statement?

Answer 39

to provide an output of true or false.

Question 40

Is else required in order to use an if statement?

Answer 40

no.

Question 41

Describe the syntax (structure) of an if statement.

Question 42

What are three logical operators?

Answer 42

logical and, logical or, logical not. &&, ||, !

Question 43

How do you compare two different expressions in the same condition?

Question 44

Why do we log things in the console?

Answer 44

to debug certain parts of our code.

Question 45

What is a method?

Answer 45

a method is a function which is a property of an object. a method could also be considered an object reference to a function.

Question 46

How is a method different from any other function?

Answer 46

methods are attributed to an object.

Question 47

How do you remove the last element from an array?

Answer 47

.pop() method

Question 48

How do you round a number down to the nearest integer?

Answer 48

Math.floor() method

Question 49

How do you generate a random number?

Answer 49

Math.random() method.

Question 50

How do you delete an element from an array?

Answer 50

.splice() method

Question 51

How do you append an element to an array?

Answer 51

.push() method

Question 52

How do you break a string up into an array?

Answer 52

.split() method

Question 53

Do string methods change the original string? How would you check if you weren't sure?

Answer 53

it doesn't change the string and you can console.log it.

Question 54

Is the return value of a function or method useful in every situation?

Answer 54

no.

Question 55

What three-letter-acronym should you always include in your Google search about a Javascript method or CSS property?

Answer 55

MDN

Question 56

What is the purpose of a loop?

Answer 56

it is a way for a function code block to keep running until it meets it requirements

Question 57

What is the purpose of a condition expression in a loop?

Answer 57

it's what stops the loop from running infinitely.

Question 58

What does "iteration" mean in the context of loops?

Answer 58

iteration is the amount of times that the loop runs.

Question 59

When does the condition expression of a while loop get evaluated?

Answer 59

before each iteration.

Question 60

When does the initialization expression of a for loop get evaluated?

Answer 60

only in the beginning and it gets checked just once.

Question 61

When does the condition expression of a for loop get evaluated?

Answer 61

it happens after the initialization and then checks the condition every time before it runs the code block

Question 62

When does the final expression of a for loop get evaluated?

Answer 62

after each iteration.

Question 63

Besides a return statement, which exits its entire function block, which keyword exits a loop before its condition expression evaluates to false?

Answer 63

break.

Question 64

What does the ++ increment operator do?

Answer 64

it increases the value by 1.

Question 65

How do you iterate through the keys of an object?

Question 66

What is JSON?

Question 67

What are serialization and deserialization?

Answer 67

converts our object into a string and deserialization is the opposite of it.

Question 68

Why serialization and deserialization useful?

Answer 68

serialization is easy to store data for later. deserialization is easy to organize and reuse data.

Question 69

How do you serialize a data structure into a JSON string using JavaScript?

Answer 69

JSON.stringify()

Question 70

How do you deserialize a JSON string into a data structure using Javascript?

Question 71

How do you store data in localStorage?

Question 72

How do you retrieve data from localStorage?

Question 73

What data type can localStorage save in the browser?

Question 74

When does the 'beforeunload' event fire on the window object?

Question 75

What is a method?

Answer 75

A method is a function which is a property of an object.

Question 76

How can you tell the difference between a method definition and a method call?

Answer 76

the method definition consists of a method header and method body while the method call method.name();

Question 77

Describe method definition syntax (structure).

Answer 77

property: function () { method body; };

Question 78

Describe method call syntax (structure).

Answer 78

method.name(arguements);

Question 79

How is a method different from any other function?

Answer 79

the method had to be associated with an object while a function isn't.

Question 80

What is the defining characteristic of Object-Oriented Programming?

Answer 80

Encapsulation. (all important information is contained inside an object and only select information is exposed.

Question 81

What are the four "principles" of Object-Oriented Programming?

Answer 81

Abstraction, encapsulation, polymorphism, and inheritance.

Question 82

What is "abstraction"?

Answer 82

hiding all but the relevant data about an object in order to reduce complexity and increase efficiency.

Question 83

What does API stand for?

Answer 83

Application programming interface.

Question 84

What is the purpose of an API?

Answer 84

API is a way for two or more computers to communicate with each other.

Question 85

What is .this in javascript?

Answer 85

refers to an object, and depends on how it's being invoked(used or called). it refers to different objects when being used.

Question 86

What does it mean to say that this is an "implicit parameter"?

Answer 86

it is available in the functions code block even though it was never included in the function's parameter list or declared with var.

Question 87

When is the value of this determined in a function; call time or definition time?

Answer 87

call time.

Question 88

How can you tell what the value of this will be for a particular function or method definition?

Answer 88

can only know if it's being called.

Question 89

How can you tell what the value of this is for a particular function or method call?

Answer 89

what object is left to the dot. otherwise it is just window.

Question 90

What kind of inheritance does the JavaScript programming language use?

Answer 90

prototype

Question 91

What is a prototype in JavaScript?

Answer 91

object that shares data

Question 92

How is it possible to call methods on strings, arrays, and numbers even though those methods don't actually exist on strings, arrays, and numbers?

Answer 92

it's within the prototype method.

Question 93

If an object does not have its own property or method by a given key, where does JavaScript look for it?

Answer 93

prototype.

Question 94

What does the new operator do?

Answer 94

the new operator makes a blank javascript object from scratch it then takes the value of the prototype property and it makes it equal to the __prototype operator. the return is the new object if there is one.

Question 95

What property of JavaScript functions can store shared behavior for instances created with new?

Question 96

What does the instanceof operator do?

Answer 96

the instanceof operator tests to see if the prototype property of a constructor appears anywhere in the prototype chain of an object. The return value is a boolean value.

Question 97

What is a "callback" function?

Answer 97

a function that is passed into another function as an argument.

Question 98

Besides adding an event listener callback function to an element or the document, what is one way to delay the execution of a Javascript function until some point in the future?

Answer 98

you can use setTimeout()

Question 99

How can you setup a function to be called repeatedly without using a loop?

Answer 99

setInterval()

Question 100

What is the default time delay if you omit the delay parameter from setTimeout() or setInterval()?

Answer 100

0

Question 101

What setTimeout() and setInterval() return?