3/21 - 3/25/2022

Question 1

What is the purpose of variables?

Answer 1

To store data

Question 2

How do you declare a variable?

Answer 2

With a keyword “var, let, or const” and a variable name.

Question 3

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

Answer 3

With the “=” assignment operator

Question 4

What characters are allowed in variable names?

Answer 4

A letter, dollar sign ($), underscore (_), or a number. It cannot start with a number.

Question 5

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

Answer 5

The lowercase and uppercase of variable names are considered.
For example, “case” and “Case” are different and would be interpreted differently by the browser/computer.

Question 6

What is the purpose of a string?

Answer 6

To store text data

Question 7

What is the purpose of a number?

Answer 7

To store numbers, perform mathematical calculations, and represent measurements

Question 8

What is the purpose of a boolean?

Answer 8

To make decisions in code

Question 9

What does the “=” operator mean in JavaScript?

Answer 9

The “=” operator is the assignment operator; it is used to assign values to variables in JavaScript.

Question 10

How do you update the value of a variable?

Answer 10

You just assign it a new value using the same name and the “=” assignment operator.

Question 11

What is the difference between null and undefined?

Answer 11

“null” means that something is nonexistent or has an invalid object or address. “null” is assigned intentionally to say that “nothing is here”.
“undefined” is a primitive value that is automatically assigned to a variable that have just been declared.

Question 12

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

Answer 12

It makes debugging easier because the labels help you keep track of which variable is which.

Question 13

Give five examples of JavaScript primitives.

Answer 13

string, numbers, boolean, undefined, and null

Question 14

What data type is returned by an arithmetic operation?

Answer 14

Number

Question 15

What is string concatenation?

Answer 15

The process of joining two or more strings together to create one string.

Question 16

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

Answer 16

The “+” operator can add numeric values or concatentate strings.

Question 17

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

Answer 17

Booleans

Question 18

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

Answer 18

It adds the current value of the variable (number or string) to the new variable (number or string) and re-assigns the result to the variable.

Question 19

What are objects used for?

Answer 19

Objects are used to group together properties and methods(functions) to create a model of something that exists in the real world.

Question 20

What are object properties?

Answer 20

Variable of an object

Question 21

Describe object literal notation.

Answer 21

Object literal notation is comprised of the keyword used to create the variable, followed by the variable name for the object, followed by curly braces with content inside. The content is comprised of the properties and their respective values.

Question 22

How do you remove a property from an object?

Answer 22

With the ‘delete’ keyword followed by the property of the object to be deleted using either dot or bracket notation.

Question 23

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

Answer 23

Using dot or bracket notation

Question 24

What are arrays used for?

Answer 24

For storing list type data

Question 25

Describe array literal notation.

Answer 25

Array literal notation consists of the variable declaration using a keyword (var, let, or const) followed by the assignment operator, followed by a set of brackets. The different data types (strings, numbers, arrays, objects) are stored inside the brackets separated by commas.

Question 26

How are arrays different from “plain” objects?

Answer 26

Arrays are ordered lists that are zero-indexed, while objects are unordered.

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 returns the number of items in the array.

Question 29

How do you calculate the last index of an array?

Answer 29

length - 1

Question 30

What is a function in JavaScript?

Answer 30

A special kind of object that is “callable”.

Question 31

Describe the parts of a function definition.

Answer 31

1. the keyword “function”
2. name of the function (optional)
3. parameters
4. opening “{“ to start the code block
5. optional “return” statement
6. closing “}” to end the code block

Question 32

Describe the parts of a function call.

Answer 32

The name of the function followed by an opening “(“ for the arguments, followed by any arguments, followed by a closing “)”.

Question 33

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

Answer 33

A function call is a “call” to execute the code block defined in the function defintion.
A function definition only defines the function; it does not execute the statements inside its code block.

Question 34

What is the difference between a parameter and an argument?

Answer 34

A parameter is used when defining a function. An argument is used when calling the function.

Question 35

Why are function parameters useful?

Answer 35

Because they act as placeholders where they can be replaced by arguments that are passed in when the function is called.

Question 36

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

Answer 36

1. It returns a value that is the result of executing the statements inside the function’s code block.
2. It stops execution at the “return” line. No code below this line is executed.

Question 37

Why do we log things to the console?

Answer 37

To keep track of what’s going on in our program/code and for debugging.

Question 38

What is a method?

Answer 38

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

Question 39

How is a method different from any other function?

Answer 39

A method is a property of an object or an object reference to a function, while a function is itself an object.

Question 40

How do you remove the last element from an array?

Answer 40

The pop method

Question 41

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

Answer 41

Math.floor() function

Question 42

How do you generate a random number?

Answer 42

The Math.random() function

Question 43

How do you delete an element from an array?

Answer 43

Using the splice() method. The splice method can take 2 or 3 arguments with the first argument being the starting index and the second argument being the number of items to delete starting from the starting index.

Question 44

How do you append an element to an array?

Answer 44

Using the push() method and specifying the element(s) to add within the parentheses

Question 45

How do you break a string up into an array?

Answer 45

Using the split() method and specifying the pattern of the split within the parentheses

Question 46

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

Answer 46

No, strings are immutable. String methods return a new string.
To check, we could console log the original string to see if the original string has been changed by a string method.

Question 47

Roughly how many string methods are there according to the MDN Web docs?

Answer 47

~50

Question 48

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

Answer 48

Not in every situation. A certain situation may require the code block of a function to execute beyond the line where a ‘return’ keyword is used (Instead of using ‘return’ in such a situation, we could console log the statement to see what value is returned as a result of execution of the line). And a return value of a method may not always be necessary as it may only be needed for testing purposes.

It would also not be useful when you’re using a method like pop or shift where you don’t care about the return value because you’re just getting rid of the item in the array.

Question 49

Roughly how many array methods are there according to the MDN Web docs?

Answer 49

~40

Question 50

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

Answer 50

MDN

Question 51

Give 6 examples of comparison operators.

Answer 51

1. >
2. <
3. ==
4. > =
5. <=
6. ===

Question 52

What data type do comparison expressions evaluate to?

Answer 52

Booleans

Question 53

What is the purpose of an if statement?

Answer 53

To evaluate whether a condition is met . If it is met, the code block immediately following it is executed.

Question 54

Is else required in order to use an if statement?

Answer 54

No

Question 55

Describe the syntax (structure) of an if statement.

Answer 55

The keyword “if” followed by an condition with a comparison (and/or logical) operator within parentheses, followed by an opening “{“ for the code block, followed by one or more statements within the code block, followed by an “}” to close the code block.

Question 56

What are the three logical operators?

Answer 56

1. &&
2. ||
3. !

Question 57

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

Answer 57

Using the && or || between the two expressions, which should each be surrounded by their own set of parentheses.

Question 58

What is the purpose of a loop?

Answer 58

To iterate over an array or the keys and/or values of properties of an object.

Question 59

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

Answer 59

To evaluate whether to execute another loop of the code block. If the condition is true, the loop will execute again; if not, it will stop execution.

Question 60

What does “iteration” mean in the context of loops?

Answer 60

To perform an execution of the code block.

Question 61

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

Answer 61

Before the first execution and after each execution to see if the condition is still true.

Question 62

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

Answer 62

It is evaluated once before the loop begins.

Question 63

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

Answer 63

After the evaluation of the initialization expression and before each loop iteration afterward.

Question 64

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

Answer 64

After each loop iteration and right before the next evaluation of the condition expression

Question 65

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

Answer 65

break

Question 66

What does the ++ increment operator do?

Answer 66

It adds one to the variable it is applied to. It is commonly applied to the counter variable of a for loop.

Question 67

How do you iterate through the keys of an object?

Answer 67

Using a ‘for…in’ loop with the syntax “${key}”