Jint

Profiling and coverage ​

UseDevTools() enables profiling when the engine is constructed:

csharp
var engine = new Engine(options => options.UseDevTools());

A CDP client can start and stop a sampled CPU profile through the Profiler domain. Chrome DevTools displays the result in its Performance tooling. Sampling is used by default; a short function that completes between sampling points might not appear.

Enable coverage ​

Coverage has a running cost and is disabled by default. Enable it explicitly at engine construction:

csharp
var engine = new Engine(options =>
    options.UseDevTools(devTools => devTools.Coverage = true));

The protocol supports precise and best-effort coverage. Declared functions that never run are reported with a zero count, so clients can show unused functions instead of omitting them.

Coverage is function-granular for unexecuted code: a statement skipped inside a function that ran may still be represented by that function's count.

Operational effects ​

  • Profiling and coverage options cannot be enabled after engine construction.
  • Precise coverage collection uses the engine's coverage counters.
  • Starting and taking precise coverage resets those counters, so an attached client can affect coverage data the host also reads.
  • Coverage enables per-statement instrumentation for all scripts, even when no client is attached.
  • Debugger support enabled by UseDevTools() also disables Jint's tight-loop optimization.

If an engine was not configured for the requested feature, the domain returns an explicit server error rather than an empty result that could be mistaken for a valid profile or uncovered script.