Jint

Error handling ​

JavaScript throws surface as JavaScriptException:

csharp
try
{
    engine.Execute("throw new TypeError('invalid input')", "rules.js");
}
catch (JavaScriptException exception)
{
    Console.WriteLine(exception.Location);
    Console.WriteLine(exception.GetJavaScriptErrorString());
}

Use the overload taking ResultLimits when error text itself must be bounded.

Promise rejection through async APIs produces the corresponding faulted Task; an explicitly unwrapped rejected promise raises PromiseRejectedException. Constraint and parsing-limit exceptions are host control flow, not catchable script errors.

CLR exceptions ​

By default, an exception from a host delegate, reflected member, or proxy trap bubbles directly to the host. The script cannot catch it:

csharp
var engine = new Engine()
    .SetValue("parse", new Action<string>(ParseDocument));

Opt in when selected CLR failures should become JavaScript Error values:

csharp
var engine = new Engine(options =>
    options.Interop.ExceptionHandler =
        exception => exception is not OperationCanceledException);

Use options.CatchClrExceptions() when every CLR exception should be converted. Cancellation, timeout, memory, statement, and recursion-limit exceptions always remain host control flow.

Script-visible messages are redacted by default. The original CLR exception remains host-only and can be recovered:

csharp
try
{
    engine.Evaluate(script);
}
catch (JavaScriptException exception)
    when (JintException.TryGetClrException(exception, out var clrException))
{
    logger.LogError(clrException, "Host call failed");
}

ExposeDetailedErrors restores host exception, loader, and overload-resolution details. Enable it only for trusted development output because messages may contain paths, URLs, type names, signatures, stack traces, or secrets.

The JavaScript error retains the original exception and everything reachable from it for as long as that error remains reachable.

Throw a JavaScript error from host code ​

Choose the matching intrinsic so script receives a real standard error:

csharp
engine.SetValue("itemAt", new Func<int, string>(index =>
{
    if ((uint) index >= (uint) items.Count)
    {
        throw new JavaScriptException(
            engine.Intrinsics.RangeError,
            $"index {index} is out of range");
    }

    return items[index];
}));

Available public error constructors include Error, RangeError, TypeError, ReferenceError, SyntaxError, EvalError, and UriError. An overload accepting a CLR exception preserves it for TryGetClrException.

Do not project a CLR exception with JsValue.FromObject and throw that value: it is not a JavaScript Error and exposes CLR exception members to script.