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JavaScript RegExp

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JavaScript RegExp is an object that represents a regular expression, which is a pattern of characters used to search, replace, and validate strings in JavaScript. The regular expression (RegExp) is an object that describes a pattern of characters.

A regular expression is created using a special syntax that consists of two forward slashes (/) enclosing the pattern that the regular expression should match.

const regex = /hello/;

We created a regular expression that matches the string “hello”.

Flags are added to the end of the regular expression after the second forward slash. For example, the i flag makes the regular expression case-insensitive.

const regex = /hello/i;

We created a case-insensitive regular expression that matches the string “hello” regardless of whether it’s uppercase or lowercase.

Regular expressions can include a variety of special characters that have special meanings. Metacharacters are characters that are interpreted in a special way by a RegEx engine. Here’s a list of metacharacters:

[] . ^ $ * + ? {} () \ |

CharacterDescription
.Matches any character except for a newline character.
*Matches the preceding element zero or more times.
+Matches the preceding element one or more times.
?Matches the preceding element zero or one time.
[]Matches any character within the brackets.
^Matches the start of the string.
$Matches the end of the string.
()Groups elements together.
|matches either the expression before or after the pipe character.

JavaScript RegExp example

Simple example code Validating the Email Address.

<!DOCTYPE html>
<html>
<body>
    <script>
        function validateEmail(email) {
        const regex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
        return regex.test(email);
    }

    console.log(validateEmail('[email protected]')); 
    console.log(validateEmail('[email protected]')); 
    console.log(validateEmail('invalid-email'));

    </script>
</body>
</html>

Output:

JavaScript RegExp

Regular Expression Flags

FlagDescription
gMatches all occurrences of the pattern within the string, rather than just the first one.
iMakes the regular expression case-insensitive, so that it matches both uppercase and lowercase letters.
mAllows the regular expression to match the start and end of each line in a multiline string, rather than just the start and end of the entire string.

JavaScript Regular Expression Methods

MethodDescription
testTests whether a string matches a regular expression pattern and returns true or false.
execSearches a string for a regular expression pattern and returns an array containing the matched substrings, or null if there is no match.
matchSearches a string for a regular expression pattern and returns an array containing the matched substrings, or null if there is no match.
searchSearches a string for a regular expression pattern and returns the index of the first match, or -1 if there is no match.
replaceSearches a string for a regular expression pattern and replaces the matched substrings with a replacement string.
splitSplits a string into an array of substrings based on a regular expression pattern.

Do comment if you have any doubts or suggestions on this JS Regular expression topic,

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.

OS: Windows 10

Code: HTML 5 Version

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