By reference to the variable. If you mutate the object's properties, the closure sees the changes. If you reassign the variable to a new object, the closure sees the new object (because it references the variable, not the original object).
The variable. A closure holds a reference to the variable, not a snapshot of its value. If the variable changes before the callback runs, the closure sees the updated value. This is why var in a loop logs the final value.
Because they all close over the same variable i. Closures capture the variable, not the value. When the callbacks run, i is the final value, so all callbacks log it.
Use let (creates a fresh binding per iteration), or an IIFE that passes the current value as a parameter (pass-by-value for primitives), or pass the value as an extra argument to setTimeout.
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