Explain lexical scoping. How does it differ from dynamic scoping?

Lexical scoping (static scoping) means a variable's scope is determined by where the function is defined in the source code, not where it is invoked.

const x = 'global'

function outer() {
  const x = 'outer'
  function inner() {
    console.log(x) // "outer" — resolved lexically
  }
  return inner
}

const fn = outer()
fn() // still "outer", not "global"

JavaScript uses only lexical scoping. The engine walks the scope chain outward from the innermost environment at write time.

Dynamic scoping (not in JS) would resolve variables based on the call stack at runtime — e.g. if inner() looked up x from whoever called it.

Why it matters

• Enables closures — inner functions reliably capture outer bindings.
• Explains this vs scope — this is dynamic (call-site), variable lookup is lexical (definition-site).
• Arrow functions inherit lexical this from their enclosing scope, unlike regular functions.

Languages with dynamic scoping (e.g. some Lisp dialects, Bash) behave differently; JavaScript developers often confuse this rules with scope rules — keep them separate in interviews.