JavaScript guide

There are two paths to Jev: the official SDK (requires Node.js 20 or newer), or plain fetch (Node.js 18+ and edge runtimes). Both hit the same endpoint.

Option 1: the official SDK

Install

npm install @typesafe-ai/sdk

example.ts

import { choice, noul, TypeSafeClient } from '@typesafe-ai/sdk';

const client = new TypeSafeClient(); // reads TYPESAFE_API_KEY; the model defaults to jev-latest

const { answers } = await client.systemOne({
  state: 'Hi, my Stripe integration keeps failing. Please refund my subscription.',
  questions: {
    department: choice('Which team should handle this', {
      billing: 'Payment or subscription issues',
      technical: 'Bugs or integration problems',
    }),
    asks_refund: noul('The customer explicitly requests a refund'),
  },
});

console.log(answers.department.choice, answers.department.confidence);
console.log(answers.asks_refund.noul);
// answers.department.choice is inferred from the criteria keys as
// "billing" | "technical" — a typo'd branch fails at compile time. That is
// what "type-safe" means once it reaches your code.

Questions are built with choice(), score(), and noul(); add model to the request to pin a version. The SDK also ships inferred answer types, a RetryPolicy (retries 408, 429, and 5xx — including 529 — by default), and structured error classes (RateLimitError, AuthenticationError, …). Repo: typesafe-ai/typesafe-sdk-js (MIT, 206★, verified 2026-09-22).

Option 2: zero-dependency fetch

Prefer no SDK? fetch the endpoint directly. The complete runnable example, triage.mjs, is a direct download (zero dependencies, Node.js 18+):

Download and run in simulated mode (offline, no key needed)

curl -O https://typesafe-jev.com/examples/javascript/triage.mjs
TYPESAFE_USE_FIXTURE=1 node triage.mjs

Real call (requires a key)

TYPESAFE_API_KEY=your-key node triage.mjs

The example asks a department Choice, a frustration Score, and a refund Noul in one request, then applies confidence thresholds to decide auto-assign versus human triage. The core:

triage.mjs (excerpt)

const response = await fetch('https://api.typesafe.ai/v1/systemone', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${process.env.TYPESAFE_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify(payload),
});
if (!response.ok) {
  // 401/422: do not retry. 429/529: exponential backoff.
  console.error(`HTTP ${response.status}: ${await response.text()}`);
  process.exit(1);
}

About the simulated mode

Fixture mode returns a fixed simulated response (output prefixed [SIMULATED]) to demonstrate parsing and routing; it is not a real API call, and this site never runs keyed code in the browser.

From the frontend?

Never bundle TYPESAFE_API_KEY into browser code. When a web UI needs Jev, have your own backend (serverless function, Worker) hold the key and expose your own API to the page. See Tool approval for a pattern.

Related pages

API reference · Python guide · Ticket triage walkthrough