Test-Driven JavaScript Development (Developer's Library)

by Christian Johansen

Unit tests should test software components in isolation. They should also run isolated—no test should ever depend on another test, tests should be able to run simultaneously and in any order.

This approach has a serious drawback in that it creates three function objects for every person object created. The original approach using a closure when adding properties to the prototype will only ever create three function objects that are shared between all circle objects. This means that creating n circle objects will cause the latter version to use approximately n times as much memory as the original suggestion. Additionally, object creation will be significantly slower because the constructor has to create the function objects as well. On the other hand, property resolution is quicker in the latter case because the properties are found directly on the object and no access to the prototype chain is needed.

notes on Crockfords module pattern

The functional style is an interesting alternative to the pseudo-classical constructors, but comes with its own limitations. The two most obvious drawbacks of this style of coding are that every object keeps its own copy of every function, increasing memory usage, and that in practice we aren’t using the prototype chain, which means more cruft when we want to call the “super” function or something similar.

drawbacks of the Module pattern / functional inheritance