function WithoutCurlyBraces() {
  if (true)
    for (let k in kv) {
        function foo() { return this }
        function bar() { return foo.call(this) }
        console.log(this, k) // => undefined
    }
}

function WithCurlyBraces() {
  if (true) {
    for (let k in kv) {
        function foo() { return this }
        function bar() { return foo.call(this) }
        console.log(this, k) // => 777
    }
  }
}