let x = 5; (function () { console.log(x); let x = 0; })()

This code will produce an error ReferenceError: Cannot access 'x' before initialization.

Why does this happen:

• Inside the function, a variable x is declared using let.
• Variables declared with let and const are in the "Temporal Dead Zone" from the start of the block until the declaration.
• When calling console.log(x), the variable x is already declared but not yet initialized, so accessing it causes an error.

If x inside the function was declared with var, the output would be undefined, because var is hoisted and initialized with undefined.

In summary: the code throws an error because of attempting to access a let variable before its declaration.