Notes JavaScript

Question 1

What must all methods have?

Answer 1

a period
method name
parentheses

Question 2

Define methods

Answer 2

They return information about an object and are called by appending an instance.

Question 3

Define Built in objects

Answer 3

Contain methods that can be called by appending the object name with a period, method name and parentheses.

Question 4

Define Template Literals

Answer 4

They are strings that allow embedded expressions ${expression}
They use back ticks instead of quotation marks. key below esc button

Question 5

What does an iteration statement do?

Answer 5

Updates the iterator each time the loop is created

Question 6

What does a stopping condition do?

Answer 6

Determines when to stop looping. It will run until the expression evaluates to false.

Question 7

What does initialization do?

Answer 7

Defines where to begin the loop by declaring (or referencing) the iterator variable.

Question 8

Define how objects execute “when passed as arguments”.

Answer 8

They are passed by reference and are therefore mutable.
The object itself is not a copy
The object is accessible and mutable inside the function.

Question 9

Define Javascript object literal value key pairs.

Answer 9

*Key-value pairs of an object can be referred to as properties.
*They are enclosed in curly brackets {}
*Values are mapped to keys in the object with a colon symbol :
*Key value pairs are separated by commas ,
*All keys are unique, VALUES are not.

Question 10

What does method Math.floor (); do?

Answer 10

Returns the largest number integer less than or equal to the given number.

Question 11

What does Math.random (); do?

Answer 11

Returns a number between 0 and 1

Question 12

Define numbers.

Answer 12

Primitive data type
include the set of all integers and floating point numbers.

Question 13

Define block scope variables.

Answer 13

The variables ‘const’ and ‘let’ are only accessible in their block or nested block.

Question 14

Define code block scope.

Answer 14

Only visible within a code block – in-between curly brackets.
{…}

Question 15

Define function scope.

Answer 15

Only visible within the function

Question 16

Define file or module scope.

Answer 16

The value/function can only be accessed from within the file.

Question 17

Define Global scope.

Answer 17

A value/function in global scope can be used anywhere in the entire program.

Question 18

Define scope.

Answer 18

Scope is a concept that refers to where values and functions can be accessed.

Question 19

Define strings.

Answer 19

They are a primitive data type
They are any grouping of characters (letters, spaces, number or symbols) surrounded by single or double quotes.

Question 20

Define console.log

Answer 20

A method that is used to log or print messages to the console.

Question 21

Define .length

Answer 21

.length is a property of the string
Returns the number of characters that make up the string
indicates the number of elements an array contains.

Question 22

Define “else block”.

Answer 22

Else block is added to a an “if” block or series of “else if” code blocks.
The “else” block will be executed only if the “if” condition fails.

Question 23

Explain what methods do.

Answer 23

Methods return information about an object.
Are called by an instance with a period.
.”the method”, name and parentheses
example: console.log ()

Question 24

Explain “undefined”.

Answer 24

Undefined is a primitive Javascript value.
It represents lack of defined value
Variables declared but not initialized will have a value undefined.

Question 25

Define “let”.

Answer 25

Creates a local variable in Javascript.
It can be re-assigned.

Question 26

What happens if you use a function with parentheses

Answer 26

The function is being called right then and there.

Question 27

What happens when you use a function without parentheses

Answer 27

The function is being assigned to the event handler, to be run later when that event happens.

Question 28

Define .map()

Answer 28

.map () executes a callback function on each element of an array.
The original array does not get altered, and the returned array may contain different elements than the original array.

Question 29

Define anonymous functions

Answer 29

Anonymous functions in Javascript do not have a name property.
They can be defined using the function keyword or as an arrow function.

Question 30

What is a “function declaration”?

Answer 30

A function body enclosed in a set of curly brackets {}.

Question 31

How are “function declarations” used?

Answer 31

Function declarations are used to create named functions.
These functions can be called using their declared name.

Question 32

What do the “function declarations” include?

Answer 32

The function keyword
The function name
Parentheses

**An optional list of parameters are separated by commas and enclosed in parentheses.

Question 33

Define function expression

Answer 33

Function expressions create functions inside an expression instead of as a function declaration.
They can be anonymous and/or assigned a variable.

Question 34

Define arguments

Answer 34

Values passed into a function when it is called.

Question 35

Define calling functions

Answer 35

Functions can be called or executed elsewhere in the code using parentheses following the function name.
When called the code inside its function body will run.

Question 36

Define “arrow function” properties.

Answer 36

Arrow function expression does not require the function keyword
=> separates the parameter from the body
Arrow functions with a single parameter
do not need parentheses around the parameter list.
Arrow functions with a single expression can use the concise function body which returns the result of the expression without sing the return keyword.

Question 37

Define Logical “NOT !” operator.

Answer 37

! will invert a boolean value
! will invert the truthiness of Non-boolean values.

Question 38

Define “break”.

Answer 38

Break is used with “switch”
If “break” is omitted from the block of a case the switch statement will continue
to check against case values until a break is encountered or the flow is broken.

Question 39

Define “case” clause.

Answer 39

Case clause is used with “switch”
If there are no matches but a default “clause” is included in the code inside then “default” will be executed.

Question 40

Define “switch statements”.

Answer 40

Provides a means of checking an expression against multiple case clauses
Case clauses should finish with a “break”.

Question 41

List the “Falsy” Values

Answer 41

False
0
empty strings
NULL
UNDEFINED
NAN

Question 42

Define logical OR || operator.

Answer 42

The || operator checks to values an returns a boolean.
If one or both values are truth, it will return TRUE.
If both are false it will return FALSE.
The button on the keyboard is above the return button used with shift key.

Question 43

Define String Interpolation.

Answer 43

String interpolation is the process of evaluating string literals containing one ore more place holders
(Expressions, variables, etc)
${…}
It can be performed using template literals
TEXT${expression}TEXT

Question 44

Define variables.

Answer 44

A variable is a container for data that can be used in the program elsewhere.
To declare a variable use these keywords with a variable name.
VAR
LET – preferred way to declare when it can be reassigned
CONST– variable with a constant value.