Logging

Observe requests, responses, and validation failures with an optional logger.

createFetch(...) accepts an optional logger?: Logger option from logger. Pass one to observe request internals; omit it and nothing is logged — zero overhead.

import { ConsoleLogger } from "@zap-studio/logger";
import { createFetch } from "@zap-studio/fetch";

const logger = new ConsoleLogger({ minLevel: "debug" });
const { api } = createFetch({ baseURL: "https://api.example.com", logger });

What Gets Logged

Event	Level	Context
A request goes out	`debug`	`method`, `url`
A 2xx response comes back	`debug`	`method`, `status`, `url`
A non-2xx response comes back	`warn`	`method`, `status`, `url`
Schema validation fails	`error`	`url`, and `error` or `issues`

A non-2xx response logs at warn instead of debug because it usually means something the caller should notice, even without throwOnFetchError turned on — without flooding debug output for every successful call.

Bring Your Own Logger

Any object implementing the Logger interface works, so you can forward these events into an existing logging setup instead of ConsoleLogger:

import type { Logger } from "@zap-studio/logger";

const logger: Logger = {
  trace: (message, context) => myBackend.log("trace", message, context),
  debug: (message, context) => myBackend.log("debug", message, context),
  info: (message, context) => myBackend.log("info", message, context),
  warn: (message, context) => myBackend.log("warn", message, context),
  error: (message, context) => myBackend.log("error", message, context),
  fatal: (message, context) => myBackend.log("fatal", message, context),
};

const { api } = createFetch({ logger });

See logger for the full Logger interface and ConsoleLogger options.