Bits of .NET

Typical bug:

for (var i = 0; i < 5; i++) {
  setTimeout(() => console.log(i), 100);
}

Output: 5 5 5 5 5

Because var is function-scoped.

✔ Fix

for (let i = 0; i < 5; i++) {
  setTimeout(() => console.log(i), 100);
}

Or:

setTimeout(((x)=>()=>console.log(x))(i), 100);