RegExp

Question 1

Regular expressions are delimited by two ____ .

Answer 1

forward slash characters.
Ex: / /

Question 2

String.prototype.match()

Answer 2

Matching an instance of a string against a regular expression and returns an array of matched values or null if no matches are found.

Question 3

What is alternation? What is the (most basic) syntax?

Answer 3

Alternation is a simple way to specify multiple alternatives for a pattern match.

The most basic syntax is two or more patterns separated by the | character and then the entire expression is surrounded by parentheses.

EX: /(cat|dog|rabbit)/

Question 4

What is a character class? What is the syntax?

Answer 4

A character class is a way to specify a set of characters that you want to match in a pattern. It allows you to define a range of characters or a list of characters that the regex engine should match against.

Character classes are denoted by enclosing the characters within [ ].

Question 5

What is a negated character class?

Answer 5

A negated character class’s first character is a ^ and matches all characters NOT identified within the character class (between [ ])

Question 6

\n

Answer 6

represents a line feed, instructing the device to move the cursor down to the next line.

Question 7

.

Answer 7

Is a meta-character that matches any character (includes whitespace, punctuation, etc..).

Note! when used inside [ ] it is interpreted as a literal period character.

Question 8

\s

Answer 8

Matches any whitespace character which includes tabs, new lines, etc.

Question 9

\S

Answer 9

Matches any NON-whitespace character.

Question 10

\d

Answer 10

Matches any decimal digit (0-9)

Question 11

\D

Answer 11

Matches any NON-decimal digit character.

Question 12

\w and \W

Answer 12

Matches ‘word characters’ which includes all alphabetic characters (a-z, A-Z), all decimal digits (0-9), and an underscore (_).

\W matches any NON-word character.

Question 13

What is an anchor?

Answer 13

Anchors provide a way to limit how a regex matches a particular string by telling the regex engine where matches can begin and where they can end.

Question 14

What anchor symbols are used to match the beginning or ending of a string?

Answer 14

The ^ matches the beginning of a string.
AKA: The entire regex must match starting at the beginning of the string.

The $ matches the ending of a string.

Question 15

m flag

Answer 15

Is a flag which has the engine treat embedded newline characters as separate lines. This has specific use case when pattern matching to the beginning or end of a string with anchors (^, $).

Question 16

A word boundary occurs…

Answer 16

1). between any pair of characters, one of which is a word character and one which is not.
2). at the beginning of a string if the first character is a word character.
3). at the end of a string if the last character is a word character.

Question 17

\b

Answer 17

Anchor that matches to word boundaries.

Question 18

*

Answer 18

Quantifier used to match 0 or more occurrences of the pattern to its left.

Question 19

+

Answer 19

Quantifier used to match 1 or more occurrences of the pattern to its left.

Question 20

?

Answer 20

Quantifier used to match 0 or 1 occurrences of the pattern to its left.

Question 21

What is a quantifier?

Answer 21

A quantifier is a meta-character that specifies the number of occurrences of a pattern.

Question 22

What is a range quantifier? What is its syntax?

Answer 22

A range quantifier is used to specify the number of occurrences of a pattern.

A range quantifier consists of a pair of curly braces {} with one or two numbers and an optional comma, which alters its behavior.

1). p{m} matches precisely m occurrences of the pattern p.
2). p{m,} matches m or more occurrences of p.
3). p{m,n} matches m or more occurrences of p, but not more than n.

Question 23

A quantifier is described as greedy when…

Answer 23

They always match the longest possible string they can.

Question 24

String.prototype.split()

Answer 24

Takes a pattern, which may be a RegExp, and divides the string into an array of substrings which is then returned.

Question 25

String.prototype.replace()

Answer 25

Returns a new string with one, some, or all matches of a pattern replaced with the replacement string.

‘I am a string’.replace(‘I am’, ‘This) will return ‘This a string’.

Question 26

In the ____ mode (by default) a quantified character is repeated as many times as ____.

Answer 26

greedy, possible

Question 27

RegExp.prototype.test()

Answer 27

takes a string as an argument and returns true if there is at least one pattern match and false otherwise.

Question 28

Explain why the following result occurs:
"Hello, Java!".match(/\bJava!\b/) ); // null (no match)

Answer 28

The reason why .match returns null is because there is no word boundary between the ! and the end of the string. A word boundary only occurs at the beginning and end of a string if the first/last character is a word character.