If you’ve spent much time writing (or debugging) JavaScript, you’ve probably come across some quirky behavior, especially in the strange and wonderful ways JavaScript handles math. How can we figure out why JavaScript behaves this way? To unravel the mystery of JavaScript addition, we will go on an empirically-structured adventure through the JavaScript web console, Mathmagic Land, and the ECMAScript Language Specification. With some help from Donald Duck, you will emerge with greater knowledge of mathematics in JavaScript, some new perspective on the methods behind the JavaScript madness, and the inspiration and tools to explore new mysteries in JavaScript yourself!