In a regular expression, match one thing or another, or both

by

The fully general method, given regexes /^A$/ and /^B$/ is:

/^(A|B|AB)$/

i.e.

/^([0-9]+|\.[0-9]+|[0-9]+\.[0-9]+)$/

Note the others have used the structure of your example to make a simplification. Specifically, they (implicitly) factorised it, to pull out the common [0-9]* and [0-9]+ factors on the left and right.

The working for this is:

  • all the elements of the alternation end in [0-9]+, so pull that out: /^(|\.|[0-9]+\.)[0-9]+$/
  • Now we have the possibility of the empty string in the alternation, so rewrite it using ? (i.e. use the equivalence (|a|b) = (a|b)?): /^(\.|[0-9]+\.)?[0-9]+$/
  • Again, an alternation with a common suffix (\. this time): /^((|[0-9]+)\.)?[0-9]+$/
  • the pattern (|a+) is the same as a*, so, finally: /^([0-9]*\.)?[0-9]+$/

More Related Contents:

  1. Split a string between special characters [closed]
  2. Not able to get Regular Expression in javascript
  3. Find String and extract with next String
  4. Regex to replace multiple spaces with a single space
  5. Regex to match all instances not inside quotes
  6. Check for special characters in string
  7. Template literal inside of the RegEx
  8. JavaScript regular expressions and sub-matches
  9. RegEx for match/replacing JavaScript comments (both multiline and inline)
  10. Restricting character length in a regular expression
  11. JavaScript regex pattern concatenate with variable
  12. javascript regular expression to check for IP addresses
  13. replace all occurrences in a string [duplicate]
  14. Passing regex modifier options to RegExp object
  15. How to ignore acute accent in a javascript regex match?
  16. Regex that can match empty string is breaking the javascript regex engine
  17. JavaScript replace/regex
  18. Regular Expression for formatting numbers in JavaScript
  19. Find all elements whose id begins with a common string
  20. Regular Expression – Extract subdomain & domain
  21. JavaScript – string regex backreferences
  22. Regular Expression for accurate word-count using JavaScript
  23. JavaScript replace \n with [duplicate]
  24. What does the forward slash mean within a JavaScript regular expression?
  25. Remove trailing numbers from string js regexp
  26. REGEX: Capture Filename from URL without file extension
  27. Replace keys in template string with object properties
  28. Convert string to Pascal Case (aka UpperCamelCase) in Javascript
  29. Regex – Repeating Capturing Group
  30. How do you split a javascript string by spaces and punctuation?

Leave a Comment