Regular expression
We have two declarations of regexp
new RegExp('template', 'flags')
/template/flags
Example
Flags
i, g, m, u, y, s
-
i uncase-sensitive
-
g search for all matches
-
m multiline mode
-
u class unicode
-
y search for specified index
-
s search for space
i
g
m
u
y
s
Metacharacters
of
template
\d \w \s \n .
-
\d - digital [0-9]
-
\w - word [a-z0-9_]
-
\s - space
-
\n - brake word
-
. - all symbols
\t \f \r \v \0 [\b] \cX \xhh \uhhhh
\u{hhhh} \u{hhhhh} \
\w
\s
\n
.
\W \S \D
-
\W - not a word
-
\D - not a digital
-
\S - not a space
\W
\D
\S
Exceptions
are also metacharacters
^ $ \b \B
^
$
\b
\B
Multiline
^
$
Quantifiers
+ * ? n{}
-
+ : one and more
-
* : zero and more
-
? : zero or one
-
n{} : spread
+
*
?
n{}
Example
Lazy and Greedy
quantifiers
Greedy (by default)
+ * ?
Lazy
+? *? ??
Sets and Ranges
[ab.fr] [12_$"]
[15] [a31-]
Sets
Example
Ranges
[1-9] [1-5]
[a-z] [a-g]
[A-Z] [1-9a-z]
[1-5A-F]
Example
We can also use metacharacters in brackets
Exclusive
Sets and Ranges
[^]
Sets
Ranges
Bracket groups
()
Example
Search engine can memorize data of bracket groups.
[0]
The first value of the variable's result will output full template pattern.
Where is this data located?
Unnecessary
Bracket groups
()?
Named group
(?<name>)
Exclusion from memory
(?:)
Backlinks in the template
Example
\n or \k<name>
Example
Example
Alterations, Lookahead and Retrospective checks
Alteration
|
Lookahead check
X(?=Y)
Negative
Lookahead check
X(?!Y)
Retrospective check
(?<=Y)X
Negative
Retrospective check
(?<!Y)X
Example
Catastrophic backtracking
Example
Example
Example
Start
Finish
2^n -1
We have two way to decide this problem.
The fist way
Reduce the number of combinations
The second way
No refunds
-
Atomic bracket groups (don't support)
-
Possessive quantifier (don't support)?
-
Lookahead (support)
Example
Example
Example
Methods & Properties
Methods
match()
matchAll()
split()
search()
replace()
Special symbol
-
$$ - insert $
-
$& - inserts all found matches
-
$' - insert a part of string before
-
$` - insert a part of string after
-
$n - inserts the contents of the nth bracket
-
$<name> - inserts the contents of the name bracket
Example
The second parameter of the replace can be a function
The parameters of the function
-
match - a match is found
-
p1 - content of brackets
-
p2 - content of brackets
-
pn - content of brackets
-
offset - position where the match was found
-
input - original string
-
groups - object with the contents of named brackets
Example
Example
Example
Example
exec()
test()
startsWith()
endsWith()
includes()
Properties
-
.flags - check by all of flags
-
.dotAll - check by s flag
-
.global - check by g flag
-
.ignoreCase - check by i flag
-
.multiline - check by m flag
-
.unicode - check by u flag
-
.sticky - check by y flag
-
.source - check by string without regexp
-
.lastIndex - it's a read/write integer property of regular expression instances that specifies the index at which to start the next match.