SOURCE

function sum(fn) {
  return function(array) {
    return fn.apply(null, array)
  }
}

console.log(sum(function(x, y) {return x + y})([1, 2]))

function exisy(x){ return x != null }

console.log(exisy(null))
console.log(exisy(undefined))
console.log(exisy(function(){}()))

function strange(n){
  for(this['i']=0;this['i']<n;this['i']++);
  return this['i']
}



console.log(strange.call({},200))