How to clone a given regular expression in JavaScript ?

Last Updated : 17 Feb, 2023

In this article, we will know How to clone a regular expression using JavaScript. We can clone a given regular expression using the constructor RegExp().

The syntax of using this constructor has been defined as follows:-

Syntax:

new RegExp(regExp , flags)

Here regExp is the expression to be cloned and flags determine the flags of the clone. There are mainly three types of flags that are used.

g:global flag with this flag the search looks for global match.
i: With this flag the search is case-insensitive.
m: With this flag we perform multi line matching.

Let us now look how we can clone a given regular expression using RegExp( ) constructor in Javascript.

Example:

HTML

<!DOCTYPE html> 
<html lang="en"> 
  <head> 
    <meta charset="utf-8" /> 
    <meta name="viewport" content="width=device-width" /> 
  
    <script src= 
"https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"> 
    </script> 
    <title>Clone a given regular expression</title> 
  </head> 
  <body style="text-align: center"> 
    <p>Enter Regular Expression to clone</p> 
  
    <input type="text" id="data" name="input" /><br /> 
    <button id="b1">Clone Regex</button> 
    <div id="display"></div> 
  
    <script> 
      function cloneRegex(input, outputflag) { 
        var pattern = input.source; 
        const flags = [...new Set(input.flags + outputflag)].join(""); 
        // Using RegExp constructor to  for cloning regular expressions, 
        // optionally while modifying flag also. 
        return new RegExp(pattern, flags); 
      } 
  
      //Taking User data as input 
      var d = $("#data").val(); 
  
      var regex = new RegExp(d, "i"); 
      //Passing user data to cloneRegex function with g set as flag. 
      var clonedregex = cloneRegex(regex, "g"); 
  
      $("#b1").click(function () { 
        $("#display").html("Cloned regex is as follows:-" + clonedregex); 
      }); 
    </script> 
  </body> 
</html> 