JavaScript 0130

Question 1

What is the purpose of variables?

Answer 1

*To have a place to store data to be used later

Question 2

How do you declare a variable?

Answer 2

using an assignment operator, e.g. “var”, and naming it within the confines of naming. it does not need to be initialized/assign to be declared

Question 3

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

Answer 3

initialize is assign. use “=” and then assign its value

Question 4

What characters are allowed in variable names?

Answer 4

$ _ letters numbers

Question 5

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

Answer 5

e.g. fullname and fullName are two different variables

Question 6

What is the purpose of a string?

Answer 6

for text content

Question 7

What is the purpose of a number?

Answer 7

store numbers to be used for things like calculation

Question 8

What is the purpose of a boolean?

Answer 8

for decision making

Question 9

What does the = operator mean in JavaScript?

Answer 9

it is used for declaring varables

Question 10

How do you update the value of a variable?

Answer 10

type its name, then “=”, then the new value

Question 11

What is the difference between null and undefined?

Answer 11

und var is not defined, null is like a placeholder

Question 12

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

Answer 12

so you can distinguish them in the console

Question 13

Give five examples of JavaScript primitives.

Answer 13

number, string, bulion, undefined, null

Question 14

What data type is returned by an arithmetic operation?

Answer 14

a number

Question 15

What is string concatenation?

Answer 15

joining data (strings?) with the + operator

Question 16

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

Answer 16

to add numbers in calculations, to join data thru concatenation

Question 17

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

Answer 17

a boolean

Question 18

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

Answer 18

it adds

Question 19

What are objects used for?

Answer 19

for storing data with descriptions, or keys/objects

Question 20

What are object properties?

Answer 20

a variable becomes a property in an object

Question 21

Describe object literal notation.

Answer 21

you create an object by using “var”, e.g., “=”, then “{“, so:

var person = {name: colin, hobby: cycling}

Question 22

How do you remove a property from an object?

Answer 22

use the delete keyword, e.g. “delete person.name”

Question 23

What are the two ways to get or update the value of a property? (give two examples of updating and two of getting)

Answer 23

bracket and dot notation, e.g.:

console.log(person.name)
console.log(person[name])

person.name = “colin”
person[“name”] = “colin”

Question 24

what’s another word for “property” in objects?

Answer 24

a property can be called a key, and with a value is called a “key value pair”

Question 25

when is bracket notation better?

Answer 25

when dealing with invalid variable names

Question 26

What are arrays used for?

Question 27

Describe array literal notation.

Question 28

How are arrays different from “plain” objects?

Answer 28

they are indexed numerically?

Question 29

What number represents the first index of an array?

Answer 29

zero

Question 30

What is the length property of an array?

Answer 30

(.length) tells us how long an array is

Question 31

How do you calculate the last index of an array?

Answer 31

.length - 1

Question 32

what is a word for “[ ]”?

Answer 32

in arrays, the brackets “[ ]” can be thought of as “at”

Question 33

what are the parts of a function’s syntax?

// [1] [2] [3]
function example(parameter1, parameter2, parameter3, …) { // [4]
// …more JavaScript code…
// [5]
return;
} // [6]

Answer 33

The function keyword to begin the creation of a new function.
An optional name. (Our function’s name is sayHello.)
A comma-separated list of zero or more parameters, surrounded by () parentheses. (Our sayHello function doesn’t have any parameters.)
The start of the function’s code block, as indicated by an { opening curly brace.
An optional return statement. (Our sayHello function doesn’t have a return statement.)
The end of the function’s code block, as indicated by a } closing curly brace.

Question 34

What is a function in JavaScript?

Answer 34

a block of lines of code which can be called to perform actions

Question 35

Describe the parts of a function definition.

Question 36

Describe the parts of a function call.

Answer 36

name of function and parentheses

Question 37

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

Answer 37

skip?

Question 38

What is the difference between a parameter and an argument?

Answer 38

parameter like placeholder
argument is what goes in placeholder

Question 39

Why are function parameters useful?

Answer 39

giving the function what it needs to run

Question 40

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

Answer 40

stops the code from running, and tells computer what to return