network (js, cli)

network is HTTP, WebSocket, and Server-Sent Events from scripts. Declare it with edge add network and import it by bare name. The same module runs in every host, in a browser, in a JS runtime such as Deno or Workers, and in the CLI, see The CLI.

The surface is fetch, fetch_text, fetch_json, abort_request, plus WebSocket (ws_open, ws_send, ws_close, ws_state) and Server-Sent Events (sse_open, sse_close, sse_state). HTTP calls suspend until the response arrives. fetch returns the full response as a JSON string with id, ok, status, headers, and body, and abort_request(id) cancels an in-flight request. fetch_text returns the body as a string and fetch_json does the same for you to parse with json.loads. Both raise on a non-2xx status. All three take an optional second argument, a JSON options string (a RequestInit). WebSocket and SSE connections open with a msg tag and stream events through receive(), with payload type values open, message, close, and error. Binary WebSocket frames surface as binary: true only. In the browser a cross-origin target must return Access-Control-Allow-Origin or the call raises, and CORS does not apply in other hosts.

SSE is built on fetch streaming, so it works in every host. It reconnects the way EventSource does, waiting the stream’s retry time and sending Last-Event-ID. An error event carries state 0 while it reconnects and 2 when the response is not an event stream, which stops it for good. Only unnamed events reach receive(), as with the message listener of EventSource, and event_id is the last id the stream sent.

WebSocket needs the runtime’s WebSocket, which browsers and JS runtimes have and the CLI does not. There ws_open raises module 'network' needs 'WebSocket', missing in this runtime.

from network import fetch, fetch_text
import json

data = json.loads(fetch("https://api.github.com/zen"))
print(data["ok"], data["status"])
print(len(fetch_text("https://api.github.com/zen")) > 0)

cmd + enter

True 200
True

Output

from network import fetch_json, fetch_text
import json

data = json.loads(fetch_json("https://api.github.com/"))
print(isinstance(data, dict))

try:
  fetch_text("https://nope.invalid/x")
except Exception as e:
  print(type(e).__name__)

cmd + enter

True
RuntimeError

Output

Hosts differ in CORS, which only the browser enforces, in WebSocket, which the CLI lacks, and in their per-host connection limits.