Cross browser default parameter values.

gistfile1.js

var def = (function () {
    var PROTO_SUPPORT = !{__proto__ : null}.toString,
        hasOwnP = {}.hasOwnProperty;
    
    var def;
    if (PROTO_SUPPORT) {
        def = function (params, func) {
            return function (args) {
                args.__proto__ = params;
                func.call(this, args);
            };
        };
    }
    else {
        def = function (params, func) {
            return function (args) {
                for (var i in params) {
                    if (hasOwnP.call(params, i) && !hasOwnP.call(args, i)) {
                        args[i] = params[i];
                    }
                }
                func.call(this, args);
            };            
        };
    }

    return def;
})();


//Example
var f = def({foo : 10, bar : 20 }, function (args) {
    print(args.foo, args.bar);
});

f({}); //10 20
f({foo : 50}); //50 20
f({foo : 50, bar : 50}); //50 50