denoland-deno/docs/runtime/web_platform_apis.md

Web Platform APIs

Deno aims to use web platform APIs (like fetch) instead of inventing a new proprietary API where it makes sense. These APIs generally follow the specifications and should match the implementation in Chrome and Firefox. In some cases it makes sense to deviate from the spec slightly, because of the different security model Deno has.

Here is a list of web platform APIs Deno implements:

fetch API

Overview

The fetch API can be used to make HTTP requests. It is implemented as specified in the WHATWG fetch spec.

You can find documentation about this API on MDN.

Spec deviations

• The Deno user agent does not have a cookie jar. As such, the set-cookie header on a response is not processed, or filtered from the visible response headers.
• Deno does not follow the same-origin policy, because the Deno user agent currently does not have the concept of origins, and it does not have a cookie jar. This means Deno does not need to protect against leaking authenticated data cross origin. Because of this Deno does not implement the following sections of the WHATWG fetch specification:
  • Section 3.1. 'Origin' header.
  • Section 3.2. CORS protocol.
  • Section 3.5. CORB.
  • Section 3.6. 'Cross-Origin-Resource-Policy' header.
  • Atomic HTTP redirect handling.
  • The opaqueredirect response type.
• A fetch with a redirect mode of manual will return a basic response rather than an opaqueredirect response.

CustomEvent, EventTarget and EventListener

Overview

The DOM Event API can be used to dispatch and listen to events happening in an application. It is implemented as specified in the WHATWG DOM spec.

You can find documentation about this API on MDN.

Spec deviations

• Events do not bubble, because Deno does not have a DOM hierarchy, so there is no tree for Events to bubble/capture through.

Web Worker API

Overview

The WebWorker API can be used to executing code in a separate thread. It is implemented as specified in the WHATWG HTML spec.

You can find documentation about this API on MDN.

Spec deviations

• Currently creating workers from blob URLs is not supported.
• Currently posted data is serialized to JSON instead of structured cloning.
• Currently object ownership cannot be transferred between workers.

Other APIs

• Blob
• Console
• FormData
• Performance
• setTimeout, setInterval, clearInterval
• Streams API
• URL
• URLSearchParams
• WebSocket

---

Typings

The TypeScript definitions for the implemented web APIs can be found in the lib.deno.shared_globals.d.ts and lib.deno.window.d.ts files.

Definitions that are specific to workers can be found in the lib.deno.worker.d.ts file.