1. A method comprising: intercepting, from a server computer, a first set of instructions that define a user interface; wherein the first set of instructions include one or more headers; stripping out the one or more headers; executing, using a headless browser, the first set of instructions without presenting the user interface to produce one or more data structures in memory; updating the one or more data structures based, at least in part, on a configuration to produce one or more updated data structures; wherein the updating comprises modifying one or more objects or operations in one or more document object model (DOM) maps in memory according to a polymorphic protocol; rendering a second set of instructions, which when executed by a client application on a client computer, cause the client computer to present the user interface, and to generate the one or more updated data structures in memory on the client computer, wherein the second set of instructions are different than the first set of instructions; wherein the second set of instructions do not include the one or more headers; sending the second set of instructions to the client computer; wherein the method is performed by one or more computing devices.