Jint

Enabling Web APIs ​

Web APIs require .NET 8 or later and are absent from a default engine.

Enable the standard non-network, non-persistent set:

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

Or select only the required features:

csharp
var engine = new Engine(options => options.UseWebApis(
    WebApiFeatures.Console |
    WebApiFeatures.Timers |
    WebApiFeatures.Encoding));

WebApiFeatures.Default includes console, timers, encoding, base64, structured clone, crypto, performance, events, URLs, files, navigator, streams, scheduling, messaging, reporting, compression, idle callbacks, global error events, and WebLocks. It deliberately excludes:

  • Fetch, EventSource, WebSocket, and XmlHttpRequest
  • Storage, CacheApi, and IndexedDb
  • FetchEvents, which lets script claim inbound requests
  • Workers, which asks the host to create engines and execution resources

Dedicated helpers such as UseFetch, UseStorage, UseCacheApi, UseWorkers, and UseWebLocks enable their flags and configure the associated options. Feature dependencies are expanded automatically; for example, fetch brings the events, URL, files, and streams surfaces it uses, and WebLocks brings navigator and events. IndexedDb brings events and structured cloning; see IndexedDB for storage lifetimes and pumping.

Performance is in the default set and installs PerformanceResourceTiming. If you also grant Fetch or XMLHttpRequest, completed requests record resource entries and queue an additional task per request, even without an observer. To omit this work, select WebApiFeatures.Default & ~WebApiFeatures.Performance before adding your network flags. This removes the clock, user timing, and observers too; see performance timeline.

Globals are installed lazily and do not replace an own global already registered by the host. Only the principal realm is changed; a ShadowRealm receives none of these globals unless the host installs them.

Enabling an existing engine ​

For a pooled engine whose needs are known per request:

csharp
WebApiFeatures added = engine.WebApi.Enable(
    WebApiFeatures.Timers | WebApiFeatures.Events);

Enable is additive. Features cannot be removed, and requesting an installed feature is a no-op. The optional configuration callback receives a private copy of that engine's web options.

Enable features before capturing a reusable global snapshot. Restoring an older snapshot removes globals installed later but does not reset the feature record, so another Enable call cannot reinstall them.

Continue with Console and timers or review Fetch and networking before granting network access. WebLocks is in the default set and grants nothing on its own; Web Locks covers the one decision it does ask a host to make, which is whether several engines share a lock space.