3 Regular Expressions traps to avoid — First published in fullweb.io issue #26

3-reg-exp-traps.md

3 Regular Expressions traps to avoid

Regular Expressions often appear daunting with their Perl-esque syntax. You will find countless tutorials online to get started, but few will highlight the traps most of us will fall into.

Note: Using JavaScript-friendly syntax

We'll be using this text:

<p>Hello <STRONG>世界</STRONG>!</p> 

1. Greedy by default

Appending ? is how to tell it not to be greedy:

/(<.*>)/ // Greedy: Returns the whole string, til the last matching > 
/(<.*?>)/ // Non-greedy: Returns up to the 1st matching >

2. Case sensitive by default

/(<strong>)/ // Returns nothing 
/(<strong>)/i // Using i flag: Returns <STRONG> 

3. Matching Unicode characters

This will return nothing:

/<strong>(\w+)<\/strong>/i

A trick consist in using \S to match anything but white space characters:

/<strong>(\S+)<\/strong>/i // Returns 世界

Note: Unicode is coming to regexp with ES6: see here »