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Fetch support for yaschema-api.

// You'll typically define this in a separate library shared by your server and clients
export const postPing = makeHttpApi({
method: 'POST',
routeType: 'rest',
url: '/ping',
isSafeToRetry: true,
schemas: {
request: {
body: schema.object({
echo: schema.string().allowEmptyString().optional()
successResponse: {
status: schema.number(StatusCodes.OK),
body: schema.string()
// Use the API via fetch to post the specified string
const doPing = async (echo?: string) => {
const pingRes = await apiFetch(postPing, { body: { echo } });
if (!pingRes.ok) {
console.error('Something went wrong', pingRes)


The above example demonstrates compile-time, type-safe use of a yaschema-api, which also performs runtime validation. With yaschema-api, both the client and server can use the same API definitions. However, it's also fine for the API definitions to be used in a one-sided way, for example, when integrating with third-party REST APIs.

With yaschema-api, types can be defined for:

  • request headers, params, query, and body
  • success response status, headers, and body
  • expected failure response status, headers, and body

yaschema-api-fetcher works out-of-the-box for web, but it can also work with node.js. To set the package up to work with node, do something like:

import nodeFetch, { Blob, FormData } from 'node-fetch';
import type { BlobConstructor, Fetch } from 'yaschema-api-fetcher';
import { setBlobConstructor, setFetch, setFormDataConstructor } from 'yaschema-api-fetcher';

setFetch(nodeFetch as Fetch);
// The following are only needed to support form-data requests
setBlobConstructor(Blob as BlobConstructor);

You should do these once around application start time, before apiFetch is used.

Thanks for checking it out. Feel free to create issues or otherwise provide feedback.

API Docs

Be sure to check out our other TypeScript OSS projects as well.