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JavaScript RegExp source Property - GeeksforGeeks

JavaScript RegExp source Property

Last Updated : 05 Aug, 2025

The source property of a JavaScript regular expression object returns the text of the pattern used to create the RegExp object, without the enclosing slashes or flags. This property is read-only and reflects the original pattern as a string.

JavaScript


 // Creating a regular expression
let regex = /hello\d+/gi;
// Accessing the source property
console.log(regex.source);

Key Points

Pattern as String: The source property returns the exact text of the pattern, making it ideal for dynamic use or debugging.
Escaped Characters: Any special characters in the pattern are escaped in the returned string.
Read-Only: The source property cannot be modified directly.

Syntax:

regex.source

Real-World Examples 1. Extracting the Pattern JavaScript


 let regex = /\d{3}-\d{2}-\d{4}/;
console.log(`Pattern used: ${regex.source}`);

Output

Pattern used: \d{3}-\d{2}-\d{4}

This is useful for logging or debugging regular expressions.

2. Reusing a Pattern JavaScript


 let regex = /[a-z]+/gi;
let anotherRegex = new RegExp(regex.source, "i");
// Reuses the pattern with a new flag
console.log(anotherRegex.test("HELLO"));

The source property allows you to reuse a regex pattern dynamically while changing its flags.

3. Building Dynamic Patterns JavaScript


 let pattern = "\\d+";
let regex = new RegExp(pattern, "g");
console.log(regex.source); 
console.log("123 456".match(regex));

Output

\d+
[ '123', '456' ]

You can dynamically construct patterns using the source property or raw strings.

4. Debugging Regular Expressions JavaScript


 let regex = /(foo|bar)\d*/gi;
console.log(`Debugging pattern: ${regex.source}`);

Output

Debugging pattern: (foo|bar)\d*

By inspecting the source, you can verify the exact regex used in your code.

5. Comparing Regular Expressions JavaScript


 let regex1 = /abc\d+/;
let regex2 = /abc\d+/g;
console.log(regex1.source === regex2.source)
console.log(regex1 === regex2);

The source property helps compare the patterns while ignoring flags or object references.

Why Use the source Property?

Dynamic Applications: Enables flexible construction of new regular expressions from existing ones.
Debugging: Helps in inspecting and validating regex patterns during development.
Pattern Reuse: Facilitates the reuse of patterns in different contexts with new flags or configurations.

Conclusion

The source property is a valuable feature for working with regular expressions in JavaScript, providing insights and enabling dynamic regex manipulation.

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