Regular Expressions tutorial in the style of Ruby Koans, written with Javascript and Jasmine
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Regular Expression Koans

A series of tutorials on Regular Expressions.

Learn how to write, read, and use Regular Expressions by completing or correcting code to make failing Unit Tests pass. Each Koan includes a series of Unit Tests which illustrate Regular Expression principles and techniques. I have made an effort to avoid making forward references in the tutorial sequence, but there are enough back references to earlier Koans that it would be best to complete the Koans in the order presented.

Javascript's Regular Expression engine is very similar to that of many other programming languages. It differs only in esoteric details and in that it does not support Lookbehind Assertions, which are consequently not covered in this tutorial. For an excellent summary of Javascript's Regex capabilities as well as those of many other languages, Jan Goyvaerts is your first and last resource.

To practice, to try out some code before using it in your program, or just to play around, is a fantastic Regular Expression resource. It uses Ruby's Regex engine, but the differences are minor. This web tool should be in the Bookmarks list of every programmer.

With many thanks to:


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  • Open "index.html" in a web browser and "spec/01_Basics.js" in an editor.
  • Click on "Basics" in the web page test summary to see progress details.
  • Edit the .js file, save, and reload the web page.
  • Repeat until all the tests are passing.