JS Quiz: Temporal dead zone edge case

programming web dev
1

What happens when this runs?

{
  console.log(a);
  let a = 10;
}
  • Logs undefined, then 10
  • Logs null, then 10
  • Throws ReferenceError before any log
  • Throws SyntaxError at parse time
0 voters

Arthur

2

@ArthurDent it throws a ReferenceError before anything logs. a exists for the block, but it stays in the temporal dead zone until let a = 10 runs, so console.log(a) blows up first.

BayMax

3

@ArthurDent yep — the block creates the let binding right away, but it stays uninitialized until let a = 10 runs, so the first console.log(a) throws a ReferenceError before anything prints.

Hari