Postcode Validation

Postcode Validation Regex

Regular Expression to match valid postcode format:

/^\s*([A-Z]{1,2}[0-9][A-Z0-9]?)\s*([0-9][ABD-HJLNP-UW-Z]{2})\s*$/i

This is according to the PAF digest as published by Royal Mail (2003).

Features:

• Leading and trailing whitespace ignored (can remove \s* from beggining and end if there is a trim() function. JS does not have one)
• OPTIONAL whitespace separating outcode and incode.
• Any separating whitespace is not pre-stripped, therefore if it is provided it can help detect invalid codes, which would by chance become valid if the space were ommited.
• Matching is case-insensitive (can remove the i flag if the case is known).
• The letters C,I,K,M,O,V never appear in the incode, and the regular expression checks this.
• The outcode and incode are reliably captured.

Shortcomings:

• If a space is not provided, and the incode is mis-typed, it may still form a valid postcode:
  • Intended: A12 3BB (A123BB without space)
  • Typed: A12BB (missed 3)
  • Matched: A1 2BB (Valid, but different postcode)
    There is no way to avoid this, it is a flaw in the design of the postcode, due to the oft-omitted space.

• Partial postcodes are not matched.
  • It would be relatively easy to make the incode optional.
  • Most applications requiring partial matches will have RM postcode data to hand, and can use that to match.