A closure is a function bundled with the lexical environment it was created in. That environment survives because the closure holds a reference to it - which is why each call to a function factory returns an independent counter.
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How JavaScript actually shares methods between objects - the prototype chain, what `new` really does, and how ES6 class syntax maps onto the same underlying machinery.
Read articleA single-rule mental model for JavaScript's `this` - everything desugars to `Function.prototype.call(thisValue, ...args)`. Walks through bare calls, method calls, detachment, `.call` / `.apply` / `.bind`, the `new` operator, arrow functions, strict mode, and how to implement `.bind` from scratch.
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