Techniques for improving server-side execution of script code include in one embodiment: receiving, at a server computer, a request from a client computer to provide a service of an application that the server computer hosts; acquiring a particular runtime from among a plurality of pre-computed runtimes in a runtime pool, each of the pre-computed runtimes in the runtime pool comprising an executable combination of computer program script code and context data that is programmed to create and use one or more data items having global scope; using the server computer, providing the request to the particular runtime and executing the particular runtime to cause generating a response to the request; transmitting the response to the client computer; cleaning up the one or more data items having global scope and returning the particular runtime to the runtime pool after completing the cleaning up.