Well, one of the challenges in writing our custom JavaScript library for this next release of our CMS at work has been to come up with a modularized approach to our objects that can be followed precisely while still allowing a measure of flexibility to the end developer (Imagine that! Actually trying to support some framework style design principles in JavaScript!). Anyway, what has been one of the most challenging pieces to the puzzle has been to appropriately handle configuration objects passed to constructors that override specific, default behavior of the object.

No, the challenge was not so much handling a config object proper — that is relatively easy. Where the challenge began to really take shape was in allowing a user to provide specific pieces of optional data and only use the valid pieces of the config object to override existing default values while ignoring the rest so as not to cause any JavaScript errors to be thrown elsewhere in the script. For a quick example, let’s say we have the following data object that loads itself up using an Ajax call (NOTE: all examples in this post are using the ExtJS lib).
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