JavaScript Foundations — The Language Itself

Deeply understand JavaScript as a programming language — not jQuery tricks, not framework syntax, but the language mechanics: closures, scope, prototypes, the event loop, coercion, `this`, and the module system. This is the foundation everything else builds on. You already understand blocks and procs — closures are the JavaScript equivalent. A Ruby block captures variables from its enclosing scope; a JavaScript closure does the same thing but is far more pervasive (every function is a closure). Ruby's `self` changes based on context; JavaScript's `this` does too, but with four different binding rules instead of Ruby's simpler model. Ruby's `require` is like JavaScript's `import`, but JS went through three module systems (CommonJS, AMD, ES Modules) before settling on one. Understanding this history explains why Node.js uses `require()` while browsers use `import`.