WHATWG Fetch

Elide exposes Blob, File, Headers, FormData, Request, Response, and fetch as globals.

Blob and File

const blob = new Blob(["hello"]);
await blob.text(); // "hello"
await blob.bytes(); // Uint8Array(5)

const file = new File(["hello"], "greeting.txt", {
  type: "text/plain",
  lastModified: 1700000000000,
});
file instanceof Blob; // true

Blob readers include text(), arrayBuffer(), bytes(), and stream(). slice() returns a Blob. File adds name and lastModified.

Headers

const headers = new Headers([["X-Custom", "1"]]);
headers.append("X-Custom", "2");
headers.get("x-custom"); // "1, 2"

headers.append("Set-Cookie", "a=1");
headers.getSetCookie(); // ["a=1"]

Names are case-insensitive. Iteration lowercases and sorts names, combines most duplicate values, and keeps Set-Cookie values separate. Invalid names or values throw TypeError. Request, response, no-CORS, and immutable guards restrict mutations where applicable.

FormData

FormData is an insertion-ordered list of string or File values.

const form = new FormData();
form.append("tag", "first");
form.append("tag", "second");
form.getAll("tag"); // ["first", "second"]

form.append("upload", new Blob(["hello"], { type: "text/plain" }));
form.get("upload").name; // "blob"

A Blob is normalized to a File when appended. set() replaces the first matching entry and removes later duplicates.

Request and Response bodies

Both classes expose body, bodyUsed, arrayBuffer(), blob(), bytes(), formData(), json(), and text().

Supported body inputs include strings, blobs, buffer sources, FormData, URLSearchParams, and ReadableStream. GET and HEAD requests reject a non-null body. A stream request body requires duplex: "half".

const request = new Request("https://example.invalid/", {
  method: "POST",
  body: "hello",
});
await request.text(); // "hello"

const response = Response.json({ ok: true });
await response.json(); // { ok: true }

Request URLs must be absolute. Response constructor statuses are limited to 200–599. Response.redirect() also requires an absolute URL. Response.error(), Response.redirect(), Response.json(), and clone() are available.

fetch

fetch(input, init?) accepts a URL, URL string, or Request and returns a Promise that resolves when response headers arrive. The response body is a ReadableStream: chunks become available before the server finishes sending the response. Methods such as response.text() consume the stream to completion.

Request bodies can also be streams. Cancelling a response body closes its network stream; an AbortSignal can cancel dispatch or subsequent body reads. Redirect modes and integrity metadata are applied during dispatch. Integrity verification buffers up to 100 MiB and completes before exposing the response.

Gzip and deflate responses are decoded once while retaining their response headers. HTTPS validates certificate chains and hostnames by default; additional trust configuration is listed in Runtime Environment Variables.

Native Image builds select Netty for HTTP/1.1 and HTTP/2; JVM mode retains the JDK backend. Use elide info to inspect the selected socket transport, TLS provider, and available linkage evidence. HTTP proxies selected by the host’s ProxySelector are supported, including HTTPS CONNECT. Authenticated proxies and unsupported proxy types fail explicitly.

Compression is documented separately in Compression Streams. HTTP server options and lifecycle belong to the Elide global reference.