Regular Expressions with Flex and ActionScript

Adobe has some great regex-based methods that can help you easily parse strings. If you aren’t familiar with regular expressions, they are basically very powerful, short-hand algorithms that are specifically designed to find patterns in strings. There are many people that hate regex’s but don’t let that deter you. They are very powerful and can save you a ton of time. And, even better is ActionScript lets you use either strings or regexes.

They are most commonly used to check form inputs for illegal characters, verifying correct formatting or for parsing complex strings. Here is an example usage pattern that looks for the end of a line:

var content:String = “Read this sentence.\r\n This is the second sentence.”;
var pattern:RegExp = /\r\n/;
var index:int =;

Here are some of the string methods you should become familiar with:

  • match() – uses either a regex or a string for the search pattern and returns an array of matching substrings.
  • replace() – does exactly what is says. It’s great for cleaning up inputs. Use cases include things such as removing inappropriate language.
  • search() – uses either a regex or a string for the search pattern and returns the first index of the substring that is located, or returns a -1. This is a great method to use for parsing strings.

Once you’ve found a match, so to speak, then you can use other string methods to parse the string:

  • slice() –  which slices out a section of the string for you given a start and ending index.
  • substr() – cuts out a substring based on a start index and length.
  • substring() – similar to substr() but the second parameter is the position of the character at the end of the substring.

A few helpful references: