How to Check if Variable is Regex in JavaScript

The term “Regex”, also known as “Regular Expression”, refers to a string of characters that creates a search pattern. It could be only one letter, a simple, or a complex pattern. A regex is used to match character combinations in strings. You can use the added search pattern to specify the search criteria to extract some information from a text. The variables can be used to store these patterns.

This manual will provide the procedure to verify if the JavaScript variable is regex.

How to Check if Variable is Regex in JavaScript?

To verify if a variable is a regex, use the JavaScript “instanceof” operator. It is utilized to determine whether the object is a specific type of instance. As it compares the instance with the type, the operator is also known as a type of Comparison operator.

If an object is an instance of a particular class, the instanceof operator gives true or false as a boolean value, depending on the situation. Moreover, it can be utilized to identify an object’s type at run time.

Syntax

Follow the below-provided syntax to use the “instanceof” operator:

regexPattern instanceof RegExp

Here, “regexPattern” is a variable that stores a regular expression or a regex, the “RegExp” is a JavaScript object that contains its own properties and methods, and the instanceof operator will check if regexPattern contains a regex or not.

Example 1: Check if Variable has a Regex Pattern

In this example, we will check whether the variable has a regex pattern. To do so, we will first create a variable named “pattern” that stores the following regex pattern or regular expression:

var pattern = /^([a-z0-9]{5,})$/;

Then, we will check whether the “pattern” variable stores any regex with the help of “instanceof” operator with a ternary (?) operator, which acts like a conditional operator and stores it in a variable called “result”:

var result = pattern instanceof RegExp ? "Yes" : "No";

Finally, print the result on the console using the “console.log()” method:

console.log(result);

As you can see that the output shows “Yes”, which indicates that the string stored in a variable “pattern” is a regex:

If you want to see how a variable follows a regex pattern, follow the next example.

Example 2: Check if Variable Follows a Regex Pattern

In this example, we will check how the variable follows a regex pattern. For this purpose, we will first create a regex pattern stored in a variable named “pattern”:

var pattern = /^([a-z0-9]{5,})$/;

Then, for verification, call the “test()” method by passing any value. If it matches the pattern, the method will return “true”; else, “false”:

console.log(pattern.test(12345));

The output displayed “true”, which means the value follows the pattern:

We have provided the simplest approach for determining if a variable is a regex in JavaScript.

Conclusion

To check if a variable is a regex, use the “instanceof” operator. It is used to check the object against a specified type. This operator outputs a boolean value based on whether or not the object is a reference of a particular class. This manual provided the procedure for verifying whether the variable is regex or not with properly defined examples.

How to Check if Variable is Regex in JavaScript