Line boundary in JavaScript regexes
There are special characters that indicate the
beginning '^' of or the end '$' of
a string. Let's see how they work with examples.
Example
In this example, the search pattern is: replace
'aaa' with '!' only if it is at the
beginning of the string:
let str = 'aaa aaa aaa';
let res = str.replace(/^aaa/g, '!');
As a result, the following will be written to the variable:
'! aaa aaa'
Example
In this example, the search pattern is: replace
'aaa' with '!' only if it is at the
end of the string:
let str = 'aaa aaa aaa';
let res = str.replace(/aaa$/g, '!');
As a result, the following will be written to the variable:
'aaa aaa !'
Example
When '^' is at the beginning of the regex,
and '$' is at the end, then in this way we
check the entire string for compliance with the regex.
In the following example, the search pattern is:
letter 'a' is repeated one or more times,
replace the whole string with '!' if it
consists of only letters 'a'.
let str = 'aaa';
let res = str.replace(/^a+$/g, '!');
As a result, the following will be written to the variable:
'!'
Practical tasks
Given a string:
let str = 'abc def xyz';
Write a regex that will find the first substring of letters.
Given a string:
let str = 'abc def xyz';
Write a regex that will find the last substring of letters.