← Functions & Closures

`this` binding

Rules that determine what `this` refers to inside a function call.

  1. new Foo() — this is the new instance.
  2. obj.method() — this is obj.
  3. fn.call(ctx) / fn.apply(ctx) / fn.bind(ctx) — this is ctx.
  4. Bare fn() — this is undefined in strict mode, the global object otherwise.
  5. Arrow functions — inherit this from the enclosing lexical scope.

Interview questions

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Why can arrow functions not be used as constructors?

They don't have their own `this` or `[[Construct]]` internal method, so `new` throws.

← Closures