Jint

Debugging ​

Create the engine with UseDevTools() before it runs any script:

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

This enables debugger support, retains source text, and treats a JavaScript debugger statement as a protocol breakpoint. These are construction-time settings; attaching an EngineTarget later cannot add them to an already-created engine.

Name source files ​

Pass a stable source name when executing scripts:

csharp
engine.Execute(
    """
    function calculate(value) {
        debugger;
        return value * 2;
    }

    calculate(21);
    """,
    "calculate.js");

Clients can then display the source and set breakpoints by URL. Absolute filesystem paths are published as file:// URLs.

Supported debugger workflows ​

The Debugger domain supports:

  • breakpoints by URL or script and possible breakpoint locations;
  • pause, resume, step into, step over, and step out;
  • continue to a location;
  • call frames and getter-free scope snapshots;
  • expression evaluation in any paused frame;
  • changing a binding with setVariableValue;
  • pausing on caught or uncaught exceptions.

The Runtime domain supports evaluation, object handles and properties, function calls, bindings, promises, console events, and exception events.

Pauses and the host thread ​

A debugger pause synchronously holds the engine thread. Jint.DevTools services pause-safe commands on that same thread until the client resumes or PauseTimeout expires. A disconnected client also releases the pause.

For HostOwned, the thread being paused is your host thread. Choose a finite PauseTimeout appropriate for the application, and keep the normal engine pump running whenever execution is not paused.

Debugger.pause takes effect at the next execution point; it cannot interrupt an indefinitely long operation inside one execution point. Configure Jint execution constraints independently.

Current limitations ​

Source maps, live source editing, frame restart, asynchronous call stacks, HeapProfiler, and per-session breakpoints are not supported. Unsupported commands return CDP method-not-found (-32601) rather than silently succeeding.