JavaScript Quiz #002

Welcome back to day 2 of #100DaysOfQuiz! Today we peek under the hood at a classic hoisting gotcha.

Question

What will the following code print?

function foo() {
  console.log(a);
  var a = 1;
  console.log(a);
}
foo();

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Short Answer

✅ Correct choice: undefined then 1

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Deep Dive – Hoisting & the Temporal Dead Zone

1. Compile-time: JavaScript moves all var declarations to the top of their function scope. Assignment stays put. So the function becomes:

   function foo() {
     var a;        // ← declaration hoisted
     console.log(a);
     a = 1;        // ← assignment stays
     console.log(a);
   }

2. Run-time: The first console.log sees the declared but un-initialised variable → undefined. After a = 1, the second console.log sees the assigned value → 1.

Key takeaway: only the declaration is hoisted, not the assignment. (With let/const you’d get a ReferenceError instead—temporal dead zone!)

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Try It Yourself – Tweak & Re-run

(Zero tracking, zero ads—just a sandbox.)

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Share & Keep Scrolling

Got it right? Brag in the replies! Follow @learn_with_san for quiz #003 tomorrow.