x.connectorsEnabled(boolean) on line 31 is a setter, return `this` for the benefit of method chaining.

That then leaves the actual definition which goes through to the JavaScript: it has an optional argument to satisfy both plausible signatures and starts on line 32.

In short, the first two are basically hints for TypeScript (if the signature is such-and-such, its return type is actually more restricted than `any`), while the third has the actual implementation.

For something similar consider how the type of callback in `addEventListener(type, callback)` depends on `type`: it’s always going to be a function taking an Event, but for e.g. type 'mousedown' it’s actually more than that, it’s a MouseEvent. So the TypeScript definitions in dom.d.ts or whatever it is (I haven’t had opportunity to actively use TypeScript for a while) has a whole lot of definitions: `addEventListener('mousedown', (event: MouseEvent) => void)`, `addEventListener('focus', (event: FocusEvent) => void)`, &c. (And because it’s just definitions, not the implementation, there is no actual implementation of `addEventListener(string, (event: Event) => void)`. This connectorsEnabled case does have the actual implementation.) In type system terms, think of it as a very restricted form of dependent typing.