MS Closure Examples

gistfile1.js

// MS example of a memory leak "caused by closure"

hookup(document.getElementById('menu'));

function hookup(element) {
  // Reference to #menu element available within 
  // mouse scope via closure
  function mouse (){}
  
  // mouse attached to #menu element via event.
  element.attachEvent( "onmouseover", mouse);
}

// --------------------------------------------------------
// MS proposed solution: Don't use closures
// (safe but not convenient or practical)

hookup(document.getElementById('menu'));

// No access to #menu element within 
// mouse scope (except via `this` keyword)
function mouse () {}

function hookup(element) {
   element.attachEvent( "onmouseover", mouse);
}

//-------------------------------------------------
// Solution 2: Create another closure 
// notice: element argument has been removed
hookup();

function hookup() {
  // Mouse has no access to element in 
  // it's scope (except through `this`)
  function mouse () {}
  
  (function(){
    // Reference creation within closure to contain scope.
    var element = document.getElementById('menu');
    element.attachEvent( "onmouseover", mouse);
  })();
  
}