Regular expressions

Today I had to fix a bug where users entered mobile phones with dashes, periods etc., and it was only legal to enter numbers. How do you fix this, you simply delete anything that isn't a number:

input_number.value = input_number.value.replace(/[^\d]/g, '');

That's it :) And I do these kind of tricks all the time.

The theory behind formal languages is also pretty interesting and I would say crucial. A lot of problems can't be solved using regular expressions. The theory of regular expressions is from 1940's! If you are more interested, here are some links to some computer science courses:

• Regularitet og Automater - The excellent Daimi course [Danish only]
• Lecture slides - from Carnegie Mellon university
• Lecture slides - from University of California, Santa Barbara

You can Google for a lot more: regular languages automata course.

xkcd comic about regular expressions: