This revives the effort for us to use ES6 features without sacrificing performance.

We'll transpile for..of statements to

for (let i = 0; i < x.length; i++) {
  const item = x[i]
}

There's a potential optimisation in here to extract x.length outside of the loop so we don't have to access length every time. Another thing we'll have to transpile is array destructuring.

With the automated approach like here we'll still have a lot of for..of where we invoke the iterator of i.e. a map.

Related to #3691