Cross-browser Getter and Setter

Question

This works in modern Chrome/Firefox/Opera but fails in IE8. Haven\'t tried it in IE9. How can I make this cross-browser compatible, including IE7+? (Fiddle here.)

Answer 1

Here is the workaround for IE6/7/8. I performed the test and it works very well!

Update: The link is broken, you can see the code of from my testing here:

    // Super amazing, cross browser property function, based on http://thewikies.com/
function addProperty(obj, name, onGet, onSet) {

    // wrapper functions
    var
        oldValue = obj[name],
        getFn = function () {
            return onGet.apply(obj, [oldValue]);
        },
        setFn = function (newValue) {
            return oldValue = onSet.apply(obj, [newValue]);
        };

    // Modern browsers, IE9+, and IE8 (must be a DOM object),
    if (Object.defineProperty) {

        Object.defineProperty(obj, name, {
            get: getFn,
            set: setFn
        });

    // Older Mozilla
    } else if (obj.__defineGetter__) {

        obj.__defineGetter__(name, getFn);
        obj.__defineSetter__(name, setFn);

    // IE6-7
    // must be a real DOM object (to have attachEvent) and must be attached to document (for onpropertychange to fire)
    } else {

        var onPropertyChange = function (e) {

            if (event.propertyName == name) {
                // temporarily remove the event so it doesn't fire again and create a loop
                obj.detachEvent("onpropertychange", onPropertyChange);

                // get the changed value, run it through the set function
                var newValue = setFn(obj[name]);

                // restore the get function
                obj[name] = getFn;
                obj[name].toString = getFn;

                // restore the event
                obj.attachEvent("onpropertychange", onPropertyChange);
            }
        };  

        obj[name] = getFn;
        obj[name].toString = getFn;

        obj.attachEvent("onpropertychange", onPropertyChange);

    }
}

Answer 2

There is a "definePropery" method that will essentially allow you to create accessor methods (getters/setters) on Objects without the need to invoke a function call like setProp() / getProp().

The syntax is a little weird but I've been able to get this to work on Firefox, Chrome, Safari and IE9.

Say I have JavaScript Object called "Person".

function Person()
{
 // set a default value //
    this.__name = 'John';
 // add getter & setter methods //
    Object.defineProperty(this, "name", {
        get: function() {
        // additional getter logic
            return this.__name;
        },
        set: function(val) {
            this.__name = val;
        // additional setter logic
        }
    });
}

var p = new Person();
console.log(p.name); // 'John'
p.name = 'Stephen';
console.log(p.name); // 'Stephen'

More info on Mozilla's site here.

Answer 3

I don't believe you can.

In IE8 and lower, property access is mere property access. There's no way to run function code without explicitly invoking the function.

I think in IE8 you may be able to with DOM elements, but I don't believe it works for regular native objects.

Answer 4

You cannot, the syntax is not supported in browsers that did not implement it. Its going to be quite a while before you'll be able to use that syntax without having CBC problems. Be grateful IE6 is pretty much dead in North America.