Function to set up a lazy populating property on an object when possible. Getting the property value will do the value calculation, then remove the getter/setter, so it behaves like a normal property. Setting the property assigns the value and removes t

gistfile1.js

// Note o must be a DOM/COM object for IE8 to work.  See below for a feature test for that.
var _define = (Object.defineProperty) ? 
    function (o, prop, fn) {
        function val(v) {
            var ret = (arguments.length) ? v : fn.call(this);

            // delete needed for IE8
            delete o[prop];
            Object.defineProperty(o, prop, {
                value: ret,
                configurable: true,
                writable: true
            });
            return ret;
        }
        Object.defineProperty(o, prop, {
            get: val,
            set: val,
            configurable: true
        });
    } : ({}.__defineGetter__) ?
        function (o, prop, fn) {
            function val(v) {
                // removes getter/setter
                delete o[prop];
                return (this[prop] = (arguments.length) ? v : fn.call(this));
            }
            o.__defineGetter__(prop, val);
            o.__defineSetter__(prop, val);
        } :
        // FIXME: this will only decrease performance over separate setup logic that just
        // calculates and assigned property values up front, so try to make sure the
        // implementation logic never takes this path.
        function (o, prop, fn) {
            o[prop] = fn.call(o);
        };

// Example
var someObject = {};

someObject.simpleProperty = 'Simple value. No need to delay this';

_define(someObject, 'complexProperty', function () {
    FunInABox.open();
    var thing1 = FunInABox.issueThing(),
        thing2 = FunInABox.issueThing();

    thing1.shakeHands();
    thing2.shakeHands();

    thing1.flyKiteIndoors();
    thing2.flyKiteIndoors();

    FunInABox.collect(thing1, thing2);
    FunInABox.close();

    return MyHouse.getState();
});


// Feature test to see if only IE8's level of support is available.  Useful to see if you
// need to set up a proxy object.
var canUseIE8Support = (function () {
    try {
        Object.defineProperty({}, 'x', {});
    } catch (ex1) {
        try {
            Object.defineProperty(document.createEventObject(), 'yes', {});
            return true;
        } catch (ex2) {}
    }
    return false;
})();