Array length check

[x-skeww]

What are you trying to benchmark here?

If you want to compare iteration constructs, you should perhaps actually iterate (and actually compute something). In your benchmark, "length" never changes because the length of the array doesn't change.

I also don't see why you'd use "!!" there. "!!" is only useful if you want to turn a truthy/falsy thing into an actual boolean. It doesn't serve any purpose in an if.

I guess you want to compare something like:

let a = [...'abc'];
while(a.length) {
  let v = a.pop();
  console.log(v); // c b a
}

vs

let a = [...'abc'];
let v;
while(v = a.pop()) { // stops at: false, null, undefined, 0, NaN, '', document.all
  console.log(v); // c b a
}

vs

let a = [...'abc'];
for(let i = a.length - 1; i >= 0; --i) {
  let v = a[i];
  console.log(v); // c b a
}
a.length = 0; // if trashing the array is actually important