Regular Expressions In JavaScript

A regular expression is a sequence of characters that specifies a text match pattern.

There are two ways to create regular expressions in JavaScript. The first is literal notation and the second is RegExp constructor.

A regular expression pattern can consist of simple characters or a combination of simple and special characters.

Regular Expressions

Glossary:

Patterns

Characters specifying a text match.

Anchors

Specify position of the match.

Flags

Modify behavior of regular expression.

Methods

Perform operations on strings.

Regular Expression Methods

Regex Methods

Name	Description	Example
String.exec()	Array containing the results of matches	str.exec(/world/);
String.match()	Array containing the results of substring	str.match(/world/);
String.replace()	Replaces specific substring with another substring	str.replace(/world/, “earth”);
String.search()	Position of occurrence of substring	str.search(/world/);
String.test()	Test whether regex matches the string	str.test(/world/);
Name	Description	Example

Regular Expression Flags

Regex Flags

Name	Description	Example
g	Global flag, finds all matches in the string	str.replace(/world/g, “earth”);
i	Ignore case flag, makes the match case-insensitive	str.replace(/World/i, “earth”);
m	Multiline flag	str.replace(/world/m, “earth”);
u	Unicode flag, handles Unicode characters correctly	str.replace(/world/u, “earth”);
Name	Description	Example

Regular Expression Anchors

Regex Anchors

Name	Description	Example
^	Matches the start of the string	str.replace(/^world/, “earth”);
$	Matches the end of the string	str.replace(/world$/, “earth”);
m	Multiline flag	str.replace(/world/m, “earth”);
\b	Matches a word boundary	str.replace(/\bworld/, “earth”);
\B	Matches a non-word boundary	str.replace(/\Bworld/, “earth”);
Name	Description	Example

Regular Expression Pattern

Regex Patterns

Name	Description	Example
.	Matches any single character	str.replace(/wo.+d/, “earth”);
\d	Matches any digit	str.replace(/d+/, “n”);
\s	Matches any whitespace character	str.replace(/\s+/g, “”);
*	Matches zero or more occurrences of the preceding element	str.replace(/worl*/, “worke”);
+	Matches one or more occurrences of the preceding element	str.replace(/\s+/g, “”);
?	Makes the preceding element optional	str.replace(/wor?l/, “worke”);
{n}	Matches exactly n occurrences of the preceding element	str.replace(/\d{3}/, “three”);
{n,m}	Matches at least n and at most m occurrences of the preceding element	str.replace(/\d{3,4}/, “three of four”);
Name	Description	Example

JavaScript Regular Expression Snippet

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// OjamboShop.com Learning JavaScript Regular Expression Tutorial
let str = `Hello world
second line hello Worlds`;
// Methods
console.log(/world/.exec(str)); // Exec
console.log(str.match(/world/)); // Match
console.log(str.replace(new RegExp("world"), "earth")); // Replace RegExp Constructor
console.log(str.replace(/world/, "earth")); // Replace Literal Notation
console.log(str.search(/world/)); // Search
console.log(/world/.test(str)); // Test
// Flags
console.log(str.replace(/world/g, "earth")); // Global
console.log(str.replace(/world/i, "earth")); // Case-insensitive
console.log(str.replace(/world/gmi, "earth")); // Multiline
// Anchors
console.log(str.replace(/^Hello/, "Hi")); // Start Of String
console.log(str.replace(/World$/, "earth")); // End Of String
console.log(str.replace(/\bWorld/, "earth")); // Beginning Of Word
console.log(str.replace(/World\b/, "earth")); // End Of Word
console.log(str.replace(/\Borld/, "orker")); // Non-word Boundary
// Pattern
console.log(str.replace(/orld?/, "orker")); // Optional Preceding Element

Usage

You can use any IDE or text editor and the web browser to compile and execute JavaScript code. For this tutorial, the OjamboShop.com Learning JavaScript Course Web IDE was used to input and compile JavaScript code for the regular expressions.

Open Source

JavaScript follows the ECMAScript standard and is licensed under the W3C Software License by web browser vendors and runtime environment vendors. This allows commercial use, modification, distribution, and allows making derivatives proprietary.

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Conclusion:

JavaScript makes it easy to use regular expressions. Use one of several built-in regular expression methods to find a substring within a string.

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