To get the result in your code, you would do:
function extend(a, b){
for(var key in b)
if(b.hasOwnProperty(key))
a[key] = b[key];
return a;
}
Keep in mind that the way you used extend there will modify the default object. If you don’t want that, use
$.extend({}, default, config)
A more robust solution that mimics jQuery’s functionality would be as follows:
function extend(){
for(var i=1; i<arguments.length; i++)
for(var key in arguments[i])
if(arguments[i].hasOwnProperty(key))
arguments[0][key] = arguments[i][key];
return arguments[0];
}