closure2.js

// Hat tip to Adam Klein for an explanation.
// v8's code generation goes through phases that roughly correspond to:
// Parse -> Analyze -> Generate Code
// During Parse/analyze, v8 tracks which variables in scope are used by closures in that scope
// All closures declared in a function keep references to any variables used by any closure
// in that function.
// In the following example, each function returned by retainTooMuch will retain bbz, even though
// the returned closure doesn't reference that variable, because another closure in the same scope
// did reference bbz.
function retainTooMuch() {
   var aaz = [1,2,3]; var bbz = [2,3,4];
   var y = () => bbz;
  return function(arg){return console.log(aaz)};
}

b = retainTooMuch();