Groups of characters in regular expressions in JavaScript
There are special commands that allow you to select
entire groups of characters at once. The command
\d denotes a digit from 0 to 9.
The \w command denotes a digit, Latin letter,
or underscore. The \s command denotes a space
or space character: space, newline, tab. You can invert
the meaning of the command by writing a capital letter:
for example, if \d is a digit, then \D
is non-digit.
Example
Let's find all the digits:
let str = '1 12 123';
let res = str.replace(/\d/g, '!');
As a result, the following will be written to the variable:
'! !! !!!'
Example
The repetition operators treat the group
commands as a single unit, i.e. grouping
parentheses are not needed. In the
following example, the search pattern looks
like this: digit from 0 to 9 one
or more times:
let str = '1 12 123 abc @@@';
let res = str.replace(/\d+/g, '!');
As a result, the following will be written to the variable:
'! ! ! abc @@@'
Example
In the following example, the search pattern looks
like this: anything one or more times, but not
a digit from 0 to 9:
let str = '123abc3@@';
let res = str.replace(/\D+/g, '!');
As a result, the following will be written to the variable:
'123!3!'
Example
In this example, the search pattern looks like this: space character once:
let str = '1 12 123 abc @@@';
let res = str.replace(/\s/g, '!');
As a result, the following will be written to the variable:
'1!12!123!abc!@@@'
Example
In this example, the search pattern looks like
this: NON-space one or more times. All
substrings separated by spaces will be
replaced with '!':
let str = '1 12 123 abc @@@';
let res = str.replace(/\S+/g, '!');
As a result, the following will be written to the variable:
'! ! ! ! !'
Example
In this example, the search pattern looks like
this: digit or letter one or more times .
All substrings consisting of digits and letters
will be replaced with '!':
let str = '1 12 123a Abc @@@';
let res = str.replace(/\w+/g, '!');
As a result, the following will be written to the variable:
'! ! ! ! @@@'
Example
In this example, the search pattern looks like
this: NON-digit and NON-letter one or more
times. In our case, '@@@' and all
spaces fall under this definition (after all,
they are neither digits nor letters.). Please
note that at the end there is one '!' -
the string ' @@@' with a space in front
was converted into it:
let str = '1 12 123 Abc @@@';
let res = str.replace(/\W+/g, '!');
As a result, the following will be written to the variable:
'1!12!123!Abc!'
Practical tasks
Given a string:
let str = 'a1a a2a a3a a4a a5a aba aca';
Write a regex that finds strings with the
letters 'a' at the edges and one digit
between them.
Given a string:
let str = 'a1a a22a a333a a4444a a55555a aba aca';
Write a regex that finds strings with the
letters 'a' at the edges and any number
of digits between them.
Given a string:
let str = 'aa a1a a22a a333a a4444a a55555a aba aca';
Write a regex that will find strings with the
letters 'a' at the edges, and any number
of digits between them (including zero digits,
that is, the string 'aa').
Given a string:
let str = 'avb a1b a2b a3b a4b a5b abb acb';
Write a regex that finds strings of the following
form: the letters 'a' and 'b'
are at the edges, and non-digit and non-space⁅/r]
between them.
Given a string:
let str = 'ave a#b a2b a$b a4b a5b a-b acb';
Write a regex that finds strings of the following
form: the letters 'a' and 'b'
are at the edges, and non-letter, non-digit,
non-space between them.
Given a string:
let str = 'ave a#a a2a a$a a4a a5a a-a aca';
Write a regex that will replace all
spaces with '!'.