JavaScript RegExp – \xnn

JavaScript regular expressions are a powerful tool that helps developers search for specific patterns within a string. One of the most useful features of these regular expressions is the ability to use escape characters to represent special characters.

One escape character that is commonly used in JavaScript regular expressions is \xnn. In this article, we will discuss what \xnn is, how it is used, and provide examples of code snippets that demonstrate its functionality.

What is \xnn?

\xnn is an escape sequence in JavaScript regular expressions that represents a character in the ASCII character set. The ‘nn’ in the sequence is a two-digit hexadecimal number that represents the ASCII code for the character.

For example, the escape sequence \x41 represents the letter ‘A’, which has an ASCII code of 65.

Using \xnn in Regular Expressions

When using \xnn in a regular expression, it is important to enclose it within a string using single or double quotes.

Here is an example of a regular expression that matches the word “cat,” where the letter “a” is represented using the \xnn escape sequence:

const regex = /c\x61t/;
const testString = 'The cat in the hat.';
const result = regex.test(testString);
console.log(result); // true

In this code snippet, the regular expression /c\x61t/ matches the string “cat” using the escape sequence \x61 to represent the letter “a”.

Matching Special Characters with \xnn

\xnn can also be used to match special characters that have special meanings in regular expressions. For example, the dot (.) character in a regular expression matches any character except for a newline. However, if you want to match a literal dot character, you can use the escape sequence \x2E.

Here is an example code snippet that demonstrates how to use \xnn to match a literal dot character:

const regex = /\x2Ecat/;
const testString = '.cat is cute';
const result = regex.test(testString);
console.log(result); // true

In this code snippet, the regular expression /\x2Ecat/ matches the string “.cat” using the escape sequence \x2E to match the literal dot character.

Matching Unicode Characters with \xnn

\xnn can also be used to match Unicode characters. To match a Unicode character using \xnn, you simply need to use the Unicode code point instead of the ASCII code.

Here is an example code snippet that demonstrates how to use \xnn to match a Unicode character:

const regex = /\u0061cat/;
const testString = 'acat is not a rat';
const result = regex.test(testString);
console.log(result); // true

In this code snippet, the regular expression /u0061cat/ matches the string “acat”. The Unicode code point for the letter “a” is 0061, which is why the escape sequence begins with “u” instead of “x”.

Conclusion

JavaScript RegExp \xnn escape sequence is a powerful tool that allows developers to match specific patterns within strings by representing characters in the ASCII character set. It can also be used to match special and Unicode characters within regular expressions.

Using \xnn in regular expressions takes the power of JavaScript to another level. We recommend that you experiment with \xnn escape sequence using the examples shown in this article to better understand its capabilities.