Undefined into Boolean

Method to get a one-time execution using an object property that starts out undefined, then is assigned True and False

by David McClelland

HTML

<input type=button value="try" onclick="testFalseOrUndefined()" />

JavaScript

thisWidget= {};
testFalseOrUndefined = function() {
alert("trying");
  if (!thisWidget.selectionUpdating) {
    alert("thisWidget.selectionUpdating: " + typeof thisWidget.selectionUpdating);
    if(thisWidget.selectionUpdating !== undefined){
      alert("thisWidget.selectionUpdating: " + thisWidget.selectionUpdating);
    }
    thisWidget.selectionUpdating = true;
    alert("thisWidget.selectionUpdating: " + thisWidget.selectionUpdating);
    setTimeout(function() {
      thisWidget.selectionUpdating = false;
      alert("thisWidget.selectionUpdating: " + thisWidget.selectionUpdating);
    }, 100);
  }
};