MongoDB's JavaScript Fuzzer is a hybrid fuzzing approach that combines "smart" and "dumb" fuzzing to produce input random enough to provoke bugs, but structured enough to pass input validation and test meaningful codepaths. The fuzzer uses tools such as LLVM's address sanitizer and undefined behavior sanitizer to detect generic coding errors, while relying on assertions within the testing target to catch application logic errors. To isolate signal from noise, the fuzzer removes branching logic via AST manipulation and wraps every single line of generated test code with a try/catch statement. The fuzzer also uses timers, print statements, and binary search scripts to triage failures quickly and correctly. By running the fuzzer in a continuous integration system, MongoDB was able to increase its coverage significantly with relatively little effort.