I used to void learning regular expression, because they looks too dry to digest. And in most case when I wanna use them, I can find existing ones on the web. But there are always a shadow in my mind that it is important. The shadow forms from when I found a lot of JavaScript books spending a whole chapter introducing Regular Expression. Weeks ago when I was reading Jeff Atwood’s Effective Programming: More Than Writing Code, I read a chapter talking about phone screen. It point out five main part in phone screen.

• Coding
• OO Programming
• Scripting and Regular Expression
• Data Structure
• Bits and Bytes

The Regular Expression hits me, and make me starting learn it. After reading the recommanded MDN Article and a video presented by Lea Verou, I start to do the sample task on Jeff’s book about Regular Expression.

A phone number match

Two kinds of phone should be matched: (123)-321-4321 and 123-321-4321.

First, the method I use is

Regex.test(String)

it will return ture if match, false if not.

Let’s do the first case. a “(” at the begining, so /(/. Then three number and a “}”, so /(\d{3})/. Then just “–” and three and four numbers, so

/\(\d{3}\)-\d{3}-\d{4}/.

In the second case, there is not “(”. So “(” should occure once or not, so add a “?”.

/\(?\d{3}\)?-\d{3}-\d{4}/.

However there is a false positive for something like 123)-321-4321. The solution is make it occur for both “(” and “)”, OR neither of them. so

/((\d{3})|(\(\d{3}\)))-\d{3}-\d{4}/

Everyone told me how powerful Regular Expressiuon is, so I guess there are much more for me to discover.