Well, you can do it like so:
(function() {
var localByaka;
Object.defineProperty(window, 'Byaka', {
get: function() {
return localByaka;
},
set: function(val) {
localByaka = window.Byaka || val;
}
});
}());
window.Byaka = "foo"; //set constant
window.Byaka = "bar"; // try resetting it for shits and giggles
window.Byaka; // will allways return foo!
If you do this as above in global scope this will be a true constant, because you cannot overwrite the window object.
I've created a library to create constants and immutable objects in javascript. Its still version 0.2 but it does the trick nicely. http://beckafly.github.io/insulatejs
