# How to clone a given regular expression in JavaScript?

JavaScript's regular expression support is widely considered to be among the best in the world, but there's one area where it's lacking: there's no built-in way to clone a regular expression. This can be a problem when you need to create a new regular expression that is similar to an existing one but with a few small changes.

The problem is that regular expressions are objects, and as such, they cannot be copied by simply assigning one to another. Consider the following code −

var regex1 = /foo/;
var regex2 = regex1;
regex2 === regex1; // true


In this code, we've created two regular expressions that are identical. But what if we want to make a small change to one of them?

regex2 = /bar/;
regex1 === regex2; // false


Now the two regular expressions are different, even though they started out as copies of each other. This is because regular expressions are mutable: they can be changed after they're created.

### Cloning using a regular expression literal

One way to clone a regular expression is to create a new regular expression literal that is similar to the existing one. For example, if we have a regular expression like this −

var regex1 = /foo/;


We can create a new regular expression that is identical to it using a regular expression literal −

var regex2 = /foo/;
regex1 === regex2; // true


This method is simple and straightforward, but it only works if the regular expression is literal (i.e. it's not created using the new RegExp() constructor).

### Cloning regular expressions with the RegExp() constructor

Another way to clone a regular expression is to use the RegExp() constructor. This allows us to create a new regular expression that is based on an existing one but with some changes. For example, if we have a regular expression like this −

var regex1 = /foo/;


We can create a new regular expression that is identical to it using the RegExp() constructor −

var regex2 = new RegExp(regex1);
regex1 === regex2; // true


This method is a bit more complex than the previous one, but it has the advantage of being able to clone regular expressions that are not literal.

### Why do we clone regular expressions?

There are a few benefits to cloning regular expressions. First, it can save you time if you need to create a lot of similar regular expressions. Second, it can help you avoid mistakes if you need to make a small change to an existing regular expression. Finally, it can make your code more readable by giving your regular expressions descriptive names.

### Disadvantage of cloning regular expressions

One disadvantage of cloning regular expressions is that it can make your code more complex. For example, if you have a regular expression like this −

var regex1 = /foo/;


And you want to create a new regular expression that is similar to it, but with the case insensitive flag set, you would need to do this −

var regex2 = new RegExp(regex1, 'i');


This is more complex than simply creating a new regular expression with the case insensitive flag set −

var regex2 = /foo/i;


In conclusion, cloning regular expressions can be a useful tool, but it comes with a few trade-offs. It can make your code more complex, but it can also save you time and help you avoid mistakes.