This talk traces JavaScript's impact on software development tools over forty years, from 1995 until 2035. Although the language is mostly dead today, it drove the largest transformation of mainstream development tools since the creation of Unix 65 years ago. We'll examine some key moments in JavaScript's history: its accidental rise to popularity; asm.js, allowing arbitrary software to run at native speed in browsers; the language ecosystem that grew up around asm.js, displacing JavaScript itself; the replacement of traditional Unix terminals, shells, and editors with new, higher-level equivalents running against the DOM; and finally, the inversion of the browser-OS relationship, still ongoing. This story is told by someone who was a fervent JavaScript detractor during its rise. It was easy to see the language's numerous and glaring shortcomings, but miss the path that it laid out.