How to load javascript in an iframe as part of the header, and we load it for child frames

To access the JavaScript of the parent frame, you simply use the parent keyword . For instance:

child.htm:

<script>
  var childVariable = 'child';

  function showParentVariable() {
    alert('from child: '+parent.parentVariable);
  }

  window.onload = function() {
    if (!!parent.child && parent.child===window) {
      parent.showChildVariable();
    }
  }
</script>

      

        
        
        
      

    

parent.htm:

<iframe src="child.htm"></iframe>
<script>
  var parentVariable = 'parent';
  var child = window.frames[0];

  function showChildVariable() {
    alert('from parent: '+child.childVariable);
  }

  window.onload = function() {
    child.showParentVariable();
  }
</script>

      

        
        
        
      

    

Here is a live demo: Child Parent

I don't know what you mean by "context sensitive".