Fetch API

About

The Fetch API provides an interface for fetching resources (including across the network). It is a more powerful and flexible replacement for XMLHttpRequest.

The Fetch API client for Hey API generates a type-safe client from your OpenAPI spec, fully compatible with validators, transformers, and all core features.

Demo

Features

• seamless integration with @hey-api/openapi-ts ecosystem
• type-safe response data and errors
• response data validation and transformation
• access to the original request and response
• granular request and response customization options
• minimal learning curve thanks to extending the underlying technology
• support bundling inside the generated output

Installation

In your configuration, add @hey-api/client-fetch to your plugins and you'll be ready to generate client artifacts. 🎉

config

export default {
  input: 'hey-api/backend', // sign up at app.heyapi.dev
  output: 'src/client',
  plugins: ['@hey-api/client-fetch'], 
};

cli

npx @hey-api/openapi-ts \
  -i hey-api/backend \
  -o src/client \
  -c @hey-api/client-fetch

TIP

This step is optional because Fetch is the default client.

Configuration

The Fetch client is built as a thin wrapper on top of Fetch API, extending its functionality to work with Hey API. If you're already familiar with Fetch, configuring your client will feel like working directly with Fetch API.

When we installed the client above, it created a client.gen.ts file. You will most likely want to configure the exported client instance. There are two ways to do that.

setConfig()

This is the simpler approach. You can call the setConfig() method at the beginning of your application or anytime you need to update the client configuration. You can pass any Fetch API configuration option to setConfig(), and even your own Fetch implementation.

import { client } from 'client/client.gen';

client.setConfig({
  baseUrl: 'https://example.com',
});

The disadvantage of this approach is that your code may call the client instance before it's configured for the first time. Depending on your use case, you might need to use the second approach.

Runtime API

Since client.gen.ts is a generated file, we can't directly modify it. Instead, we can tell our configuration to use a custom file implementing the Runtime API. We do that by specifying the runtimeConfigPath option.

export default {
  input: 'hey-api/backend', // sign up at app.heyapi.dev
  output: 'src/client',
  plugins: [
    {
      name: '@hey-api/client-fetch',
      runtimeConfigPath: './src/hey-api.ts', 
    },
  ],
};

In our custom file, we need to export a createClientConfig() method. This function is a simple wrapper allowing us to override configuration values.

hey-api.ts

import type { CreateClientConfig } from './client/client.gen';

export const createClientConfig: CreateClientConfig = (config) => ({
  ...config,
  baseUrl: 'https://example.com',
});

With this approach, client.gen.ts will call createClientConfig() before initializing the client instance. If needed, you can still use setConfig() to update the client configuration later.

createClient()

You can also create your own client instance. You can use it to manually send requests or point it to a different domain.

import { createClient } from './client/client';

const myClient = createClient({
  baseUrl: 'https://example.com',
});

You can also pass this instance to any SDK function through the client option. This will override the default instance from client.gen.ts.

const response = await getFoo({
  client: myClient,
});

SDKs

Alternatively, you can pass the client configuration options to each SDK function. This is useful if you don't want to create a client instance for one-off use cases.

const response = await getFoo({
  baseUrl: 'https://example.com', // <-- override default configuration
});

Interceptors

Interceptors (middleware) can be used to modify requests before they're sent or responses before they're returned to your application. They can be added with use, removed with eject, and updated wth update. The use and update methods will return the id of the interceptor for use with eject and update. Fetch API does not have the interceptor functionality, so we implement our own. Below is an example request interceptor

use

import { client } from 'client/client.gen';
// Supports async functions
async function myInterceptor(request) {
  // do something
  return request;
}
interceptorId = client.interceptors.request.use(myInterceptor);

eject

import { client } from 'client/client.gen';

// eject interceptor by interceptor id
client.interceptors.request.eject(interceptorId);

// eject interceptor by reference to interceptor function
client.interceptors.request.eject(myInterceptor);

update

import { client } from 'client/client.gen';

async function myNewInterceptor(request) {
  // do something
  return request;
}
// update interceptor by interceptor id
client.interceptors.request.update(interceptorId, myNewInterceptor);

// update interceptor by reference to interceptor function
client.interceptors.request.update(myInterceptor, myNewInterceptor);

and an example response interceptor

use

import { client } from 'client/client.gen';
async function myInterceptor(response) {
  // do something
  return response;
}
// Supports async functions
interceptorId = client.interceptors.response.use(myInterceptor);

eject

import { client } from 'client/client.gen';

// eject interceptor by interceptor id
client.interceptors.response.eject(interceptorId);

// eject interceptor by reference to interceptor function
client.interceptors.response.eject(myInterceptor);

update

import { client } from 'client/client.gen';

async function myNewInterceptor(response) {
  // do something
  return response;
}
// update interceptor by interceptor id
client.interceptors.response.update(interceptorId, myNewInterceptor);

// update interceptor by reference to interceptor function
client.interceptors.response.update(myInterceptor, myNewInterceptor);

TIP

To eject, you must provide the id or reference of the interceptor passed to use(), the id is the value returned by use() and update().

Auth

The SDKs include auth mechanisms for every endpoint. You will want to configure the auth field to pass the right token for each request. The auth field can be a string or a function returning a string representing the token. The returned value will be attached only to requests that require auth.

import { client } from 'client/client.gen';

client.setConfig({
  auth: () => '<my_token>', 
  baseUrl: 'https://example.com',
});

If you're not using SDKs or generating auth, using interceptors is a common approach to configuring auth for each request.

import { client } from 'client/client.gen';

client.interceptors.request.use((request, options) => {
  request.headers.set('Authorization', 'Bearer <my_token>'); 
  return request;
});

Build URL

If you need to access the compiled URL, you can use the buildUrl() method. It's loosely typed by default to accept almost any value; in practice, you will want to pass a type hint.

type FooData = {
  path: {
    fooId: number;
  };
  query?: {
    bar?: string;
  };
  url: '/foo/{fooId}';
};

const url = client.buildUrl<FooData>({
  path: {
    fooId: 1,
  },
  query: {
    bar: 'baz',
  },
  url: '/foo/{fooId}',
});
console.log(url); // prints '/foo/1?bar=baz'

Custom fetch

You can implement your own fetch method. This is useful if you need to extend the default fetch method with extra functionality, or replace it altogether.

import { client } from 'client/client.gen';

client.setConfig({
  fetch: () => {
    /* custom `fetch` method */
  },
});

You can use any of the approaches mentioned in Configuration, depending on how granular you want your custom method to be.

API

You can view the complete list of options in the UserConfig interface.

Examples

You can view live examples on StackBlitz.

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