1. A system comprising: one or more computers; and a computer-readable medium coupled to the one or more computers having instructions stored thereon which, when executed by the one or more computers, cause the one or more computers to perform operations comprising: accessing historical usage data pertaining to one or more past interactions between a user and a resource; determining, using the historical usage data, that, on average, the user accesses a first feature of the resource that is associated with a first code module more frequently than the user accesses a second feature of the resource that is associated with a second code module, then adjusting a mapping for the resource to associate an initial load event with the first code module, and to associate an event other than an initial load event with the second code module, wherein the mapping identifies one or more events that, upon occurrence, will trigger a dynamic loading of one or more code modules that are referenced by the resource; determining that a particular event has occurred; identifying one or more of the code modules that are associated with the particular event, based on the adjusted mapping; and dynamically loading the identified code modules.