Commonly used methods of regular expressions in typescript

Here are some commonly used regular expression metacharacters:

^: Match the beginning of the string.
$: Match the end of the string.
.: Match any single character except line breaks.
*: Match the previous characters zero or multiple times.
+: Match the previous characters once or more times.
?: Match the previous characters zero or once.
[]: Match any character in square brackets.
[^]: Match any character not in square brackets.
(): Group matching, you can use \1, \2, etc. to reference the group later.
| : Match any expression on the left and right sides
{}: indicates the number of match repetitions, which specifies the number of times the matching character or subexpression occurs. For example, {3} means that the previous character or subexpression appears exactly 3 times, {2,5} means that the previous character or subexpression appears 2 to 5 times, and {2,} means that the previous character or subexpression appears at least 2 times.
\d: Match any numeric character, equivalent to [0-9].
\w: Match any letter, number or underscore character, which is equivalent to [A-Za-z0-9_].
\s: Match any whitespace character, including spaces, tabs, line breaks, etc.

Here are some commonly used regular expression flags:

i: Ignore case.
g: Global matching.
m: Multiple row matching.

TypeScript supports regular expression syntax in JavaScript, so we can use regular expressions in JavaScript to match strings. In TypeScript, we can use the RegExp class to create regular expression objects.

The syntax for creating a regular expression object is as follows:

let regex = new RegExp('pattern', 'flags');

Where 'pattern' is the pattern we want to match and 'flags' is an optional flag that specifies the behavior of a regular expression.

For example, we can create a regular expression object that matches all numbers:

let regex = new RegExp('\\d+');

In the example above, '\d+' is a pattern that matches one or more numbers. We use double backslashes to escape special characters in regular expressions.

We can also use literal syntax to create regular expression objects:

let regex = /\d+/;

In the example above, /\d+/ is a regular expression literal, which is equivalent to the RegExp object we created earlier.

Once we create a regular expression object, we can use it to match the string. We can use the test() method of the RegExp object to test whether a string matches a regular expression:

let regex = /\d+/;
let str = '123';
if ((str)) {
  ('Match!');
} else {
  ('No match.');
}

In the example above, we use the test() method to test if the string '123' matches the regular expression /\d+/. Since the string '123' contains numbers, the test returns true and outputs 'Match!'.

We can also use the exec() method of the RegExp object to find substrings in the string that match the regular expression:

let regex = /\d+/g;
let str = '123 abc 456 def';
let match;
while ((match = (str)) !== null) {
  (match[0]);
}

In the example above, we use the exec() method to find all substrings in the string that match the regular expression /\d+/. Since we use the 'g' flag in our regular expressions, this method will look for all matches. In a while loop, we use the match variable to store the result of the current match. If the exec() method returns null, it means there are no more matches.

In the example above, we use match[0] to access the first result of the match. If there are capture groups in our regular expression, they can be accessed using match[1], match[2], etc.

The RegExp class provides many ways to manipulate regular expressions

test() method: test whether the string matches the regular expression.

let regex = /hello/gi;
let str = 'Hello World';
((str)); // true

exec() method: Find matching regular expressions in a string.

let regex = /hello/gi;
let str = 'Hello World';
((str)); // ['Hello']

match() method: Find a matching regular expression in a string, returning an array or null.

let regex = /hello/gi;
let str = 'Hello World';
((regex)); // ['Hello']

replace() method: replaces the matching regular expression in the string.

let regex = /hello/gi;
let str = 'Hello World';
((regex, 'Hi')); // 'Hi World'

search() method: Find a matching regular expression in a string and return the matching position.

let regex = /hello/gi;
let str = 'Hello World';
((regex)); // 0

Properties of regular expressions:

The RegExp class also provides some properties to get information about regular expressions.

source attribute: Get the source code of the regular expression.

let regex = /hello/gi;
(); // 'hello'

flags attribute: Gets the flag for the regular expression.

let regex = /hello/gi;
(); // 'gi'

Code demo:

let regex = /hello/gi;
let str = 'Hello World';
((str)); // true
((str)); // ['Hello']
((regex)); // ['Hello']
((regex, 'Hi')); // 'Hi World'
((regex)); // 0
(); // 'hello'
(); // 'gi'

Output result:

true
['Hello']
['Hello']
'Hi World'
0
'hello'
'gi'

Hopefully this information will help you better understand how to use regular expressions in TypeScript.

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