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Harness all the power of your backend's OpenAPI v3 spec files by generating a client object in a few lines


🚀 Creates at runtime a client object in a few lines (read more in Getting Started)

// Creation
import { createClient } from 'oa-client';
const client = createClient(specs, callers, {
  origin: '',
  validationLevel: 'error',
// Usage
client[/* path */][/* method */](/* optional params */).then(apiResponse => { /* ... */ })

🚀 Optionally throws for invalid path, query, or body

# OpenAPI specs
        - in: path
          name: userId
            type: integer
client["/users/{userId}"].get({ pathParams: { userId: "john" } });
// throws [oa-client:103] Data does not pass validation: data.userId should be an integer

🚀 Compiles the path and query params

  pathParams: { job: "director" },
  queryParams: { name: "Gaspar Noé" },
// calls /new-user/director?name=Gaspar+No%C3%A9

Getting started

1. Install the package

npm install --save oa-client

2. Import the package

This package is isomorphic: it can be used both as an ESM or a CommonJS

// ok
import { createClient } from "oa-client";
// also ok
const { createClient } = require("oa-client");

3. Have somewhere your OpenAPI specs as a JS object

You don't need to add anything compared to normal specs, except for an optional .paths[path][method]['x-type'], that defines the caller, more on them below. If this key is omitted, its value defaults to the request type (e.g. "get" or "post").

Note that oa-client does not resolve specs for you. If you have $refs, you should use a package like json-schema-ref-parser to resolve them.

const specs = {
  openapi: "3.0.0",
  info: {
    /* ... */
  paths: {
    "/users/{userId}": {
      get: {
        "x-type": "authorizedGet", // will use the "authorizedGet" caller
        parameters: [
            in: "path",
            name: "userId",
            required: true,
            schema: {
              type: "integer",
        responses: {
          /* ... */
    "/status": {
      get: {
        // no x-type -> will use the "get" caller
        responses: {
          /* ... */

4. Write your callers

These are generic functions that handle requests at the HTTP level.

They are not handled by this package, because they can be very different from one codebase to another; but usually you don't have to write a lot of them.

url is an URL, body is a plain JS object.

const callers = {
  get: async (url) => {
    const resp = await fetch(url);
    const json = await resp.json();
    return json;
  authorizedGet: async (url) => {
    const headers = new Headers();
    headers.append("Content-Type", "application/json");
    headers.append("Authorization", `Bearer ${localStorage.token}`);
    const resp = await fetch(url, { headers });
    const json = await resp.json();
    return json;
  authorizedPost: async (url, body) => {
    const headers = new Headers();
    headers.append("Content-Type", "application/json");
    headers.append("Authorization", `Bearer ${localStorage.token}`);
    const resp = await fetch(url, {
      method: "POST",
      body: JSON.stringify(body),
    const json = await resp.json();
    return json;

5. Create your client

You do this once and client can be used in the rest of your code afterward.

origin defaults to specs.servers[0].url. Optional if it's defined, else required.

validationLevel is one of 'off' (default), 'warn', or 'error'. It checks the path params, the query params, and the body against the schema present in the specs.

const client = createClient(specs, callers, {
  origin: "",
  validationLevel: "error",

6. Use your client

Thereafter, oa-client does all the work of building the full URL and validating input data for you!

In this example, this

const data = await client["/users/{userId}"].get({
  pathParams: { userId: 123 },

is equivalent to

const url = new URL("");
const data = await callers.authorizedGet(url);

Differences with openapi-client

The openapi-client package is similar but accomplishes things differently.

openapi-client is a code generation package. You use it as a command line so that it consumes OpenAPI specs and outputs code that will call your server. It is not ideal because you don't own and control all of your code, and it adds complexity.

oa-client is simpler - it exposes createClient, a factory that take specs as input and builds the client at runtime. If your API updates, you don't have to write or generate a single line of code.

openapi-client handles all the HTTP calls and authentication for you. That can seem powerful, but actually the system is very rigid, even for small customizations, and doesn't cover all cases you'll face along the way.

In oa-client, you fully own your generic HTTP callers: you write them yourself, but you probably won't write more than five of them during your whole project lifetime: who needs more than get, post, authorized get, authorized post and file upload?

| Written with <3 by Nino Filiu |
|  Contributions are welcomed!  |
         \   ^__^
          \  (oo)\_______
             (__)\       )\/\
                 ||----w |
                 ||     ||


Flexible client helper for making and validating calls to OpenAPI backends. For Node and the browser. Runtime lib - no need for code generation!