How to get value from Object, with default value

Generally, one can use the or operator to assign a default when some variable evaluates to falsy:

var foo = couldBeUndefined || "some default";

so:

var arg1 = config.args.arg1 || "test";
var arg2 = config.args.arg2 || "param2";

assuming that config.args is always defined, as your example code implies.