L1: String Methods, for while loops

Question 1

What does String.prototype.concat() mutate/return?

Answer 1

Returns new string, basically the same as going caller + argument

Question 2

Can .concat take multiple arguments

Answer 2

yes
basically argument + argument + argument

Question 3

What does String.prototype.includes() mutate/return?

Answer 3

Returns boolean if the caller contains the substring

Question 4

What does the optional second argument do in String.prototype.includes()

Answer 4

Indicates with index to start looking from

Question 5

What does String.prototype.split() do if there’s no argument?

Answer 5

Just gives the full string in an array.

Question 6

What does String.prototype.trim() mutate/return?

Answer 6

returns string with caller’s whitespaces, newlines \n, and tabs \t remove

Question 7

method to only remove spaces from beginning or end

Answer 7

.trimStart()
.trimEnd()

Question 8

Return boolean if a string contain a substring

Answer 8

.includes()

Question 9

Return the character at a certain index of a string (2 ways)

Answer 9

.charAt(2)
or
‘string’[2]

Question 10

What’s the difference between .charAt and ‘string’[2]in regard to whether the character exists

Answer 10

‘string’[2] will return undefined if that index doesn’t exist
.charAt will return an empty string.

Question 11

Return the Unicode code point or character code for a given index of a string

Answer 11

‘abcdef’.charCodeAt(1)

Question 12

Create a character for a given char code argument

Answer 12

String.fromCharCode(97)

Question 13

Why are some methods prototypes and some not? like
String.fromCharCode(97)
‘a’

Answer 13

It’s a common pattern in different languages to write methods that don’t pertain to a specific value of a type directly on the class/constructor for that type. In this case, fromCharCode isn’t an operation you’d perform on a string value. That is, something like the following doesn’t make sense:
‘abcd’.fromCharCode(97)

Question 14

Return boolean if a string ends or starts with a certain substring

Answer 14

String.prototype.endsWith
String.prototype.startsWith

Question 15

Return a string a number of times

Answer 15

String.prototype.repeat

Question 16

Is a while loop or a for loop preferred for iterating ove rcollections?

Answer 16

for loop

Question 17

Why would a for/in loop give a different result from a whlie loop (with Object.keys() ethod) for iterating over object keys?

Answer 17

for/in is that it iterates over the properties of an object’s prototypes as well:

Question 18

When might you use:
while (true) {
if (str.length >= 10) {
break;
}

over
while (str.length < 10)
or do while?

Answer 18

When you want to break in the middle of a loop.

Question 19

What is a guard clause

Answer 19

conditional statement that protects the body of a loop or function from having to deal with values it doesn’t need to handle.
Generally continue, break, or return.

Question 20

Generally you should use blocks for if statements and not single lines. t or f?
Are there any exceptions

Answer 20

T
Single lines are ok for guard clauses, like
if (numbers[index] % 2 === 1) continue;

Instead of
if (numbers[index] % 2 === 1) {
continue;
}

Question 21

Convert single digit string number ‘1’ to a number using charcode

Answer 21

‘123’.charCodeAt(2) - ‘0’.charCodeAt(0)

Question 22

Fill the start or end of a string with a certain string to a certain string length.
What happens if you try to fill with a string that is longer than the specified remaining string length?

Answer 22

.padStart()
.padEnd()

It trims the filler string. It always goes to the target length.

Question 23

What do these returns if the index is outside the range of the string:
charAt, charCodeAt, ‘asdf’[6]

Answer 23

charAt- undefined
charCodeAt- undefined
‘asdf’[6]- undefined

Question 24

What happens if string .includes uses a negative index for the second parameter

What about array.includes with negative inde second parameter

Answer 24

Seems to just search from the beginning with strings

With arrays, still searches forward, but does the whole -index + length