JavaScript \xxx Metacharacter | Find Character using Octal Number

The JavaScript \xxx metacharacter is used when we need to match a character using its octal number (in the form xxx), while working with JavaScript regular expressions. For example:

HTML with JavaScript Code

<!DOCTYPE html>
<html>
<body>

   <p id="xyz"></p>

   <script>
      let myString = "JavaScript is Fun.";
      let pattern = /\165/;
      document.getElementById("xyz").innerHTML = myString.search(pattern);
   </script>
   
</body>
</html>

Output

In the above example, the following JavaScript statement:

let myString = "JavaScript is Fun.";

defines a string variable "myString" with the value "JavaScript is Fun." Then a regular expression variable pattern that matches the Unicode code point for the lowercase letter "u" is defined through the second JavaScript statement:

let pattern = /\165/;

In octal notation, the code point is represented as 165. Now using the following or the third JavaScript statement:

document.getElementById("xyz").innerHTML = myString.search(pattern);

The search() method is invoked on the myString variable with the pattern variable as an argument. The search() method looks for the first occurrence of the pattern in the string and returns the index of the match. And then sets the innerHTML property of the HTML element with the ID "xyz" to the search() method result.

Since the octal value 165 refers to u, and the index of u in the string is 15. Therefore, the program has produced 15 as output.

Note: The search() method is used to search a substring (value) in a string using a regular expression.

Now, before closing the discussion on the "\xxx" metacharacter when working with the JavaScript RegEx, I'm willing to include one more example with proper comments to explain the codes in the program itself. So here is the example program demonstrating the "\xxx" metacharacter in JavaScript RegEx.

HTML with JavaScript Code

<!DOCTYPE html>
<html>
  <body>
    <p id="demo"></p>

    <script>
      // Define a string with octal escape sequences
      const myString = "\101\102\103";

      // Define a pattern that matches any uppercase letter
      const myPattern = /[A-Z]/;

      // Test the pattern against the string
      const isMatch = myPattern.test(myString);

      // Display the result in the HTML document
      document.getElementById("demo").innerHTML = isMatch;
    </script>
  </body>
</html>

Output

true

In this example, we define a string myString with octal escape sequences \101\102\103, which is equivalent to the string "ABC". We then define a regular expression pattern myPattern that matches any uppercase letter using the character class [A-Z].

We test the pattern against the string using the test() method and store the result in the isMatch variable. Finally, we display the result in the HTML document by setting the innerHTML property of the "p" element with the id "demo".

JavaScript Online Test

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