Primitive Types Module #17

Question 1

How would you define a number using hexadecimal syntax?

Answer 1

Start with the 0x prefix.

Question 2

How would you convert $10.00 so that the calculations are dependably exact?

Answer 2

Multiply by 100 ( 10 x 100 = 1000 ) Stripe uses this method and essentially dollar values are calculated in pennies. .01 === 1

Question 3

How can you test for a “type” of a variable?

Answer 3

Use the "typeof" keyword. For example:
const age = Number( 36 )
typeof age //number

Question 4

How can an you create an object from a number type?

Answer 4

Use the "new" keyword in front of the number. For Example: 
const age = new Number ( 36 )
typeof age //object

Question 5

What can you use to determine the original number value of an object?

Answer 5

METHOD

Use the value of method. Example:
age.valueOf ( )

Question 6

Define EPSILON.

Answer 6

EPSILON is the smallest interval between two numbers.

Question 7

Define MAX_SAFE_INTEGER.

Answer 7

MAX_SAFE_INTEGER is the maximum integer value JavaScript can represent.

Question 8

Define MAX_VALUE.

Answer 8

MAX_VALUE is the maximum positive value that JavaScript can represent.

Question 9

Define MIN_SAFE_INTEGER.

Answer 9

MIN_SAFE_INTEGER is the minimum integer value JavaScript can represent.

Question 10

Define MIN_VALUE.

Answer 10

MIN_VALUE is the minimum positive value JavaScript can represent.

Question 11

Define NaN

Answer 11

A special value representing “not a number”.

Question 12

METHODS: How is the NaN method expressed in JavaScript?

Answer 12

Number.isNaN(value) returns true if value is not a number

Question 13

METHODS: How is the finite number method expressed?

Answer 13

Number.isFinite(value): returns true if value is a finite number.

Question 14

METHODS: How is the integer method expressed ?

Answer 14

METHOD

Number.isInteger(value): returns true if value is an integer.

Question 15

METHODS: How is the “safe” integer method expressed ?

Answer 15

METHOD

Number.isSafeInteger(value): returns true if value is a safe integer.

Question 16

METHODS: How is the floating point number method expressed?

Answer 16

Number.parseFloat(value): converts value to a floating point number and returns it.

Question 17

METHODS: How is the value of a floating point number converted into an integer expressed as a method?

Answer 17

Number.parseInt(value): converts value to an integer and returns it. It can also convert strings with words, extracting the first number, but the string must start with a number.

Question 18

What kinds of methods can you use on a “Number Object”?

Answer 18

.toExponential( ), .toFixed( ), .toLocaleString( ), .toPrecision( ), .toString( ), .valueOf( )

Question 19

What’s another way to define a string other than quotes? What’s it called?

Answer 19

By using backticks this is called a template literal. This relieves the need to escape double or single quotes with backslashes.

Question 20

How would you insert a variable or expression into a string?

Answer 20

“By using ${ dollarsign-curly brace syntax with backticks arouund it all } Inside the braces you can add any JS expression.”

Question 21

What is charAt( i )

Answer 21

It is a method that returns the character at the position of i in a string. 
Examples:
"Flavio".charAt(0) //'F'
"Flavio".charAt(1) //'l'
"Flavio".charAt(2) //'a'

Question 22

What is concat (str)? What does it do?

Answer 22

Concatenates the current string with the string str. For example:
“Flavio”.concat(“ “).concat(“Copes”) //’Flavio Copes’

Question 23

What does endsWith(str) do?

Answer 23

Check if a string ends with the value of the string str. Example:
“JavaScript”.endsWith(“Script”) //true
“JavaScript”.endsWith(“script”) //false

Question 24

What does includes(str) do?

Answer 24

Check if a string includes the value of the string str.
“JavaScript”.includes(“Script”) //true
“JavaScript”.includes(“script”) //false
“JavaScript”.includes(“JavaScript”) //true
“JavaScript”.includes(“aSc”) //true
“JavaScript”.includes(“C++”) //false

includes() also accepts an optional second parameter, an integer which indicates the position where to start searching for:

“a nice string”.includes(“nice”) //true
“a nice string”.includes(“nice”, 3) //false
“a nice string”.includes(“nice”, 2) //true

Question 25

What does this return?

inexOf(str)

Answer 25

Gives the position of the first occurrence of the string str in the current string. Returns -1 if the string is not found.

Examples:
"JavaScript".indexOf("Script") //4
"JavaScript".indexOf("JavaScript") //0
"JavaScript".indexOf("aSc") //3
"JavaScript".indexOf("C++") //-1

You can pass a second parameter to set the starting point:

“a nice string”.indexOf(“nice”) !== -1 //true
“a nice string”.indexOf(“nice”, 3) !== -1 //false
“a nice string”.indexOf(“nice”, 2) !== -1 //true

Question 26

What does this method return?

lastIndexOf(str)

Answer 26

Gives the position of the last occurrence of the string str in the current string.

For example:
“JavaScript is a great language. Yes I mean JavaScript”.lastIndexOf(“Script”) //47
“JavaScript”.lastIndexOf(“C++”) //-1

Question 27

What does this return?

padEnd( )

Answer 27

METHOD

The purpose of string padding is to add characters to a string, so it reaches a specific length.

padEnd( ), introduced in ES2017, adds such characters at the end of the string.

padEnd(targetLength [, padString])

Sample usage:
padEnd( ) 	
‘test’.padEnd(4) 	‘test’
‘test’.padEnd(5) 	‘test ‘
‘test’.padEnd(8) 	‘test    ‘
‘test’.padEnd(8, ‘abcd’) 	‘testabcd’

Question 28

What does this return?

padStart( )

Answer 28

METHOD

Like padEnd( ), we have padStart( ) to add characters at the beginning of a string.

padStart(targetLength [, padString] )

Sample usage:
padStart( ) 	
‘test’.padStart(4) 	‘test’
‘test’.padStart(5) 	‘ test’
‘test’.padStart(8) 	‘    test’
‘test’.padStart(8, ‘abcd’) 	‘abcdtest’

Question 29

What does this method return?

repeat( )

Answer 29

METHOD

Introduced in ES2015, repeats the strings for the specificed number of times:

“Ho”.repeat(3) //’HoHoHo’

Returns an empty string if there is no parameter, or the parameter is 0. If the parameter is negative you’ll get a RangeError.

Question 30

What does this return?

replace(str1, str2)

Answer 30

METHOD

Find the first occurrence of str1 in the current string and replaces it with str2 (only the first!). Returns a new string.

“JavaScript”.replace(“Java”, “Type”) //’TypeScript’

You can pass a regular expression as the first argument:

“JavaScript”.replace(/Java/, “Type”) //’TypeScript’

replace( ) will only replace the first occurrence, unless you use a regex as the search string, and you specify the global (/g) option:

“JavaScript JavaX”.replace(/Java/g, “Type”) //’TypeScript TypeX’

The second parameter can be a function. This function will be invoked for every match found, with a number of arguments:

the string that matches the pattern
an integer that specifies the position within the string where the match occurred
the string

The return value of the function will replace the matched part of the string.

Example:

“JavaScript”.replace(/Java/, (match, index, originalString) => {
console.log(match, index, originalString)
return “Test”
}) //TestScript

This also works for regular strings, not just regexes:

“JavaScript”.replace(“Java”, (match, index, originalString) => {
console.log(match, index, originalString)
return “Test”
}) //TestScript

Question 31

What does this return?

search(str)

Answer 31

Return the position of the first occurrence of the string str in the current string.

It returns the index of the start of the occurrence, or -1 if no occurrence is found.

“JavaScript”.search(“Script”) //4
“JavaScript”.search(“TypeScript”) //-1

Question 32

What does this return?

slice(begin, end)

Answer 32

METHOD

The slice( ) method extracts a section of a string and returns it as a new string, without modifying the original string.

The second param (end) is optional.

“This is my car”.slice(5) //is my car
“This is my car”.slice(5, 10) //is my

if you set a negative first parameter, the start index starts from the end, and the second parameter must be negative as well, always counting from the end:

“This is my car”.slice(-6) //my car
“This is my car”.slice(-6, -4) //my

const str = ‘The quick brown fox jumps over the lazy dog.’;

console.log(str.slice(31));
// expected output: "the lazy dog."

console.log(str.slice(4, 19));
// expected output: "quick brown fox"

console.log(str.slice(-4));
// expected output: "dog."

console.log(str.slice(-9, -5));
// expected output: "lazy"

Question 33

What returns from this method?

split(separator)

Answer 33

METHOD

You can use the split() function when you want to turn a string into an array of substrings.

The parameter of the split( ) function is your separator. Each time the split( ) function finds the separator in the string, it starts a new array element.

The separator itself gets omitted and won’t be part of the array elements.

For example if you have a string “dog,cat,mouse” and you would like to have an array with the elements “dog”, “cat” and “mouse”, you could use split(“,”) for that:

const stringAnimals = "dog,cat,mouse"
const arrayAnimals = stringAnimals.split(",")

Question 34

What does this return?

startsWith(str)

Answer 34

METHODS

Check if a string starts with the value of the string str

You can call startsWith( ) on any string, provide a substring, and check if the result returns true or false:

“testing”.startsWith(“test”) //true
“going on testing”.startsWith(“test”) //false

This method accepts a second parameter, which lets you specify at which character you want to start checking:

“testing”.startsWith(“test”, 2) //false
“going on testing”.startsWith(“test”, 9) //true

Question 35

What does this method return?

substring( )

Answer 35

substring( ) returns a portion of a string and it’s similar to slice( ), with some key differences.

If any parameter is negative, it is converted to 0. If any parameter is higher than the string length, it is converted to the length of the string.

So:

“This is my car”.substring(5) //’is my car’
“This is my car”.substring(5, 10) //’is my’
“This is my car”.substring(5, 200) //’is my car’
“This is my car”.substring(-6) //’This is my car’
“This is my car”.substring(-6, 2) //’Th’
“This is my car”.substring(-6, 200) //’This is my car’

Question 36

What is returned when using this method?

toLowerCase( )

Answer 36

METHOD

Return a new string with the text all in lower case.

Same as toLocaleLowerCase( ), but does not consider locales at all.

“Testing”.toLowerCase( ) //’testing’

Question 37

What is returned while using this method?

toString( )

Answer 37

Returns the string representation of the current String object:

const str = new String("Test")
str.toString() //'Test'

Same as valueOf( ).

Question 38

What’s returned when using this method?

toUpperCase( )

Answer 38

METHOD

Return a new string with the text all in upper case.

Same as toLocaleUpperCase(), but does not consider locales at all.

“Testing”.toUpperCase( ) //’TESTING’

Question 39

What is returned from this method?

trim( )

Answer 39

Return a new string with removed white space from the beginning and the end of the original string

“Testing”.trim( ) //’Testing’
“ Testing”.trim( ) //’Testing’
“ Testing “.trim( ) //’Testing’
“Testing “.trim( ) //’Testing’

Question 40

What’s returned from this method?

trimEnd( )

Answer 40

Return a new string with removed white space from the end of the original string

“Testing”.trimEnd() //’Testing’
“ Testing”.trimEnd() //’ Testing’
“ Testing “.trimEnd() //’ Testing’
“Testing “.trimEnd() //’Testing’

trimRight() is an alias of this method.

Question 41

What is this?
const isReal = Boolean(true)

Answer 41

the Boolean( ) factory function

Question 42

What is this?

const isReal = true

Answer 42

The boolean literal syntax

Question 43

What are falsy values?

Answer 43

Falsy values, values interpreted as false, are

0 - 0
NaN
undefined
null
;("") //empty string

All the rest is considered a truthy value.