closured-scope-mutation.js

const fs = []
for(var i = 0; i < 3; ++i) {
  fs.push(() => console.log(i))
}
fs.forEach(f => f())

// with explicit scope

const fs = []
const scope = { i: 0 }
for(; scope.i < 3; ++scope.i) {
  fs.push(() => console.log(scope.i))
}
fs.forEach(f => f())

The Ruby version:

for i in 0..3
  fs << lambda { puts i }
end
fs.each {|f| f.call()}