Regular expression for Dutch zip / postal code

Question

I'm trying to build a regular expression in javascript to validate a Dutch zipcode.

The zipcode should contain 4 numbers, then optionally a space and then 2 (case insensitive) letters

Valid values:

1001aa  
1001Aa  
1001 AA

I now have this, but it does not work:

var rege = /^([0-9]{4}[ ]+[a-zA-Z]{2})$/;

Answer 1

Edited to handle no leading 0 requirement for Dutch postal codes, and to eliminate matches for SS, SA, and SD. This should do it all for you.

Final regex:

var rege = /^[1-9][0-9]{3} ?(?!sa|sd|ss)[a-z]{2}$/i;

Fiddle unit test: http://jsfiddle.net/hgU3u/

Here's a breakdown:

1. ^ matches beginning of string
2. [1-9][0-9]{3} matches a single non-zero digit, and three 0-9 digits
3. ? matches 0 or 1 spaces (you could use * to match 0 or more spaces)
4. (?!sa|sd|ss) is a lookahead test to check that the remainder is not "sa", "sd", or "ss".
5. [a-z]{2} matches 2 a-z characters
6. $ matches the end of the string
7. i at the end is the case-insensitive modifier