When working on personal projects, I often find myself repeatedly looking up the same regular expressions—email validation, URLs, dates, digits, whitespace removal, and more.
Here’s a collection of practical, copy-and-paste–ready regex snippets that frequently appear across projects.
The examples use JavaScript/TypeScript, but almost all of them work in any mainstream language.
- 1. Email validation (practical version)
- 2. URL validation (http/https)
- 3. Digits only (integer)
- 4. Remove all whitespace
- 5. Working with comma-formatted numbers
- 6. Basic phone number check (Japan)
- 7. Alphanumeric only
- 8. Alphanumeric + specific safe symbols
- 9. Japanese characters only (Hiragana, Katakana, Kanji)
- 10. ISO8601 date (YYYY-MM-DD)
- 11. Extract file extension
- 12. Remove simple HTML tags
- 13. Collapse multiple newlines into one
- 14. Trim whitespace from start/end (regex version)
- 15. Extract Markdown links
- Summary
1. Email validation (practical version)
Not fully RFC-complete—just the most usable option for real-world apps.
^[^\s@]+@[^\s@]+\.[^\s@]+$
Example:
const isEmail = (value: string) =>
/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(value);
2. URL validation (http/https)
^https?:\/\/[^\s/$.?#].[^\s]*$
A balanced pattern that works well in most applications without being overly strict.
3. Digits only (integer)
^\d+$
Allow negative and floating-point numbers:
Negative + decimal allowed
^-?\d+(\.\d+)?$
4. Remove all whitespace
\s+
Usage:
value.replace(/\s+/g, "");
5. Working with comma-formatted numbers
Remove all commas
,/g
Insert commas every 3 digits
value.replace(/\B(?=(\d{3})+(?!\d))/g, ",");
6. Basic phone number check (Japan)
If you work with Japanese phone numbers:
^0\d{1,4}-?\d{1,4}-?\d{3,4}$
Flexible and practical for most use cases.
7. Alphanumeric only
^[A-Za-z0-9]+$
Useful for user IDs, passwords, etc.
8. Alphanumeric + specific safe symbols
^[A-Za-z0-9._-]+$
Common for filenames, slugs, and usernames.
9. Japanese characters only (Hiragana, Katakana, Kanji)
^[\p{Hiragana}\p{Katakana}\p{Han}]+$
JavaScript requires the u flag:
/^[\p{Hiragana}\p{Katakana}\p{Han}]+$/u
10. ISO8601 date (YYYY-MM-DD)
^\d{4}-\d{2}-\d{2}$
With time:
YYYY-MM-DDTHH:MM:SSZ
^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?Z$
11. Extract file extension
\.([0-9A-Za-z]+)$
Example:
const ext = filename.match(/\.([0-9A-Za-z]+)$/)?.[1];
12. Remove simple HTML tags
Not perfect for complex HTML, but great for lightweight cleanup.
<[^>]+>
text.replace(/<[^>]+>/g, "");
13. Collapse multiple newlines into one
\n{2,}
Usage:
text.replace(/\n{2,}/g, "\n");
14. Trim whitespace from start/end (regex version)
^\s+|\s+$
Useful if you’re working inside a pipeline where trim() isn’t suitable.
15. Extract Markdown links
\[(.*?)\]\((.*?)\)
Extracts both the link text and URL.
Summary
These regex snippets cover the common cases you’ll see again and again in personal projects:
- Validation (email, URL, numbers, alphanumerics)
- Text cleaning (whitespace, newlines)
- Parsing (extensions, Markdown, HTML)
