In June 2024, we held the 73rd edi­tion of the “JavaScript the Lan­guage” meet­up, where each month we dive into one of JavaScript’s fea­tures, some make you go, “Wait, it does what now?” We do this by writ­ing tests, read­ing the spec­i­fi­ca­tion, and run­ning those tests – the pro­gram­ming equiv­a­lent of a work­out that actu­al­ly makes you stronger.

Here’s the plan: We start by brain­storm­ing ques­tions we can answer with code. Then, we write a test with a descrip­tion so clear even your non-cod­ing gold­fish could fol­low it. Before we run this test, we open the ECMAScript spec­i­fi­ca­tion, which is like the sacred scrolls of JavaScript knowl­edge, to see if our wild guess—I mean, hypothesis—is cor­rect. For exam­ple, does "".at(-1) return an emp­ty string or unde­fined? (Spoil­er alert: It’s a fun sur­prise every time!) This deep dive often leads us into the labyrinth of JavaScript’s inner work­ings, where we encounter delight­ful odd­i­ties and bril­liant design choic­es. By the time we run the test, we’ve either con­firmed our the­o­ry or had an exis­ten­tial cri­sis about how com­put­ers work, which we then call “learn­ing”.

Join me in this ses­sion to expe­ri­ence the joy of team pro­gram­ming, the thrill of test­ing, and the sheer geeky plea­sure of read­ing the spec. Even if you cur­rent­ly think test­ing is as excit­ing as watch­ing paint dry, I promise you’ll leave with a new­found appre­ci­a­tion for it—or at least a few good laughs. Let’s embark on this adven­ture togeth­er and unlock the mys­ter­ies of how JavaScript ticks, one test at a time.