Web Platform APIs

    Here is a list of web platform APIs Deno implements:

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

    You can find documentation about this API on MDN.

    • 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 .
      • 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.
    • The specification is vague on how . Firefox is the only mainstream browser that implements fetching file: URLs, and even then it doesn’t work by default. As of Deno 1.16, Deno supports fetching local files. See the next section for details.
    • The request and response header guards are implemented, but unlike browsers do not have any constraints on which header names are allowed.
    • The referrer, referrerPolicy, mode, credentials, cache, integrity, , and window properties and their relevant behaviours in RequestInit are not implemented. The relevant fields are not present on the Request object.
    • Request body upload streaming is supported (on HTTP/1.1 and HTTP/2). Unlike the current fetch proposal, the implementation supports duplex streaming.
    • The set-cookie header is not concatenated when iterated over in the headers iterator. This behaviour is in the process of being specified.

    Deno only supports absolute file URLs, this means that fetch("./some.json") will not work. It should be noted though that if is specified, relative URLs use the --location as the base, but a file: URL cannot be passed as the --location.

    To be able to fetch some resource, relative to the current module, which would work if the module is local or remote, you would want to use import.meta.url as the base. For example, something like:

    Notes on fetching local files:

    • Permissions are applied to reading resources, so an appropriate --allow-read permission is needed to be able to read a local file.
    • Fetching locally only supports the GET method, and will reject the promise with any other method.
    • A file that does not exists simply rejects the promise with a vague TypeError. This is to avoid the potential of fingerprinting attacks.
    • No headers are set on the response. Therefore it is up to the consumer to determine things like the content type or content length.
    • Response bodies are streamed from the Rust side, so large files are available in chunks, and can be cancelled.

    You can find documentation about this API on MDN.

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

    Definitions that are specific to workers can be found in the file.