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JavaScript RegExp toString() Method - GeeksforGeeks

Last Updated : 05 Dec, 2024

The RegExp.toString() method in JavaScript is used to return the string representation of a regular expression object. It converts the regular expression to a string, including its pattern and flags.

let reg1 = /hello/i;
let reg2 = /\d{3}-\d{2}-\d{4}/;

console.log(reg1.toString());
console.log(reg2.toString());

/hello/i
/\d{3}-\d{2}-\d{4}/

• toString() method: This method converts the regular expression into a string that includes both the pattern and the flags.
• For reg1, the result is "/hello/i", showing the regular expression pattern and the case-insensitive flag (i).
• For reg2, the result is "/\\d{3}-\\d{2}-\\d{4}/", showing the pattern for matching an SSN. Note that backslashes in the pattern are escaped when printed.

Syntax

let regexString = regex.toString();

• regex: The regular expression object.
• regexString: The string representation of the regular expression, including the pattern and any flags.

Now Let's see some of the uses of RegExp toString() Method

The toString() method is particularly useful for debugging when you need to log or inspect the regular expression in its literal string format. Here’s an example:

let regex = /^[A-Za-z0-9]+$/; 

console.log("Regex pattern:", regex.toString()); 

Regex pattern: /^[A-Za-z0-9]+$/

This output makes it easier to verify that the regex pattern is what you expected.

If you're generating regular expressions dynamically based on user input or other conditions, toString() can be helpful to view or log the constructed regex:

let pattern = "\\d{3}-\\d{2}-\\d{4}";
let regex = new RegExp(pattern, "g");

console.log(regex.toString());

/\d{3}-\d{2}-\d{4}/g

This shows how the dynamically created regular expression looks when converted to a string.

• Readable Output: Converts the regular expression object into a string format, making it easy to view and understand.
• Includes Flags: The flags (like g, i, m) are included in the string output, which is helpful when inspecting the regex behavior.
• Escape Sequences: Special characters (like backslashes) are escaped in the output string, making it easier to read and understand.
• Helpful for Debugging: Great for logging and debugging regular expressions during development.

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