  Client-side Javascript execution environments (browsers) allow anonymous
functions and event-based programming concepts such as callbacks. We
investigate whether a mutate-and-test approach can be used to optimise web page
load time in these environments. First, we characterise a web page load issue
in a benchmark web page and derive performance metrics from page load event
traces. We parse Javascript source code to an AST and make changes to method
calls which appear in a web page load event trace. We present an operator based
solely on code deletion and evaluate an existing "community-contributed"
performance optimising code transform. By exploring Javascript code changes and
exploiting combinations of non-destructive changes, we can optimise page load
time by 41% in our benchmark web page.
