Transforming data on fetch

All network requests flow through the fetch() method, so any transforms needed can simply be done by overriding it with a call to super.

tip

Note: If you retain control over the API design, generally it's preferred to update the data sent over the network. Keeping the client as thin as possible is helpful to both performance and complexity.

That said, in many cases you want to consume APIs you don't have control over - be they public APIs, or due to internal organizational structure.

Snakes to camels

Commonly APIs are designed with keys using snake_case, but many in typescript/javascript prefer camelCase. This snippet lets us make the transform needed.

CamelResource.ts
import { camelCase, snakeCase } from 'lodash';
import { RestEndpoint, RestGenerics  } from '@data-client/rest';

function deeplyApplyKeyTransform(obj: any, transform: (key: string) => string) {
  const ret: Record<string, any> = Array.isArray(obj) ? [] : {};
  Object.keys(obj).forEach(key => {
    if (obj[key] != null && typeof obj[key] === 'object') {
      ret[transform(key)] = deeplyApplyKeyTransform(obj[key], transform);
    } else {
      ret[transform(key)] = obj[key];
    }
  });
  return ret;
}

class CamelEndpoint<O Extends RestGenerics = any> extends RestEndpoint<O> {
  getRequestInit(body) {
    // we'll need to do the inverse operation when sending data back to the server
    if (body) {
      return super.getRequestInit(deeplyApplyKeyTransform(body, snakeCase));
    }
    return super.getRequestInit(body);
  }
  process(value) {
    return deeplyApplyKeyTransform(value, camelCase);
  }
}

Deserializing fields

In many cases, data sent through JSON is serialized into strings since JSON only has a few primitive types. Common examples include ISO 8601 for dates or even strings for decimals that require high precision (floats can be lossy). Keeping data in the serialized form is often fine, especially if it is only being used to be displayed. However, this can be problematic when derived data is computed like adding time to a date or multiplying two numbers.

In this case, simply use the static schema with Temporal.Instant and BigNumber

Fixtures

GET /price/btc-usd

{"exchangePair":"btc-usd","price":"32982389239823983298329832.238923982389328932893298","updatedAt":"2023-12-12T19:26:09.439Z"}

▶api/Price.ts

import BigNumber from 'bignumber.js';

export class ExchangePrice extends Entity {
  exchangePair = '';
  updatedAt = Temporal.Instant.fromEpochSeconds(0);
  price = new BigNumber(0);
  pk() {
    return this.exchangePair;
  }
  static key = 'ExchangePrice';

  static schema = {
    updatedAt: Temporal.Instant.from,
    price: BigNumber,
  };
}
export const getPrice = new RestEndpoint({
  path: '/price/:exchangePair',
  schema: ExchangePrice,
});

▶PricePage.tsx

import { getPrice } from './api/Price';

function PricePage() {
  const currentPrice = useSuspense(getPrice, {
    exchangePair: 'btc-usd',
  });
  return (
    <div>
      ${currentPrice.price.toFormat(2)} as of{' '}
      <time>
        {DateTimeFormat('en-US', { dateStyle: 'medium' }).format(
          currentPrice.updatedAt,
        )}
      </time>
    </div>
  );
}
render(<PricePage />);

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Deserializing Date

In case you want to use legacy Date, you can turn the constructor into a function schema.

export class ExchangePrice extends Entity {
  exchangePair = '';
  updatedAt = new Date(0);
  price = new BigNumber(0);
  pk() {
    return this.exchangePair;
  }
  static key = 'ExchangePrice';

  static schema = {
    updatedAt: iso => new Date(iso),
    price: BigNumber,
  };
}

Case of the missing `Id`

You now want to interface with a great new streaming site called mystreamsite.tv. It has a simple API to retireve information about current streams. You can get a stream with the url pattern https://mystreamsite.tv/[username]/. However, for some reason they don't return the username in the response body! You want to be able to refer to it and it's the only uniquely defining identifier for the class.

We can simply parse the username from the request url itself and add that to the response.

GET https://mystreamsite.tv/ntucker/
{
  "title": "When I'm Grandmaster, I will play faster.",
  "game": "Starcraft II",
  "current_viewers": 1337,
  "live": true
}

api/Stream.ts
const USERNAME_MATCHER = /.*\/([^\/]+)\/?/;

class Stream extends Entity {
  username = '';
  title = '';
  game = '';
  currentViewers = 0;
  live = false;

  pk() {
    return this.username;
  }
  static key = 'Stream';
}

const getStream = new RestEndpoint({
  urlPrefix: 'https://mystreamsite.tv',
  path: '/:username',
  schema: Stream,
  process(value, { username }) {
    value.username = username;
    return value;
  },
});

Ticker prices

Ticker

AssetPrice

import { Entity, RestEndpoint } from '@data-client/rest';

export class Ticker extends Entity {
  product_id = '';
  trade_id = 0;
  price = 0;
  size = '0';
  time = Temporal.Instant.fromEpochSeconds(0);
  bid = '0';
  ask = '0';
  volume = '';

  pk(): string {
    return this.product_id;
  }
  static key = 'Ticker';

  static schema = {
    price: Number,
    time: Temporal.Instant.from,
  };
}

export const getTicker = new RestEndpoint({
  urlPrefix: 'https://api.exchange.coinbase.com',
  path: '/products/:productId/ticker',
  schema: Ticker,
  process(value, { productId }) {
    value.product_id = productId;
    return value;
  },
  pollFrequency: 2000,
});

import { useLive } from '@data-client/react';
import { getTicker } from './Ticker';

function AssetPrice({ productId }: Props) {
  const ticker = useLive(getTicker, { productId });
  return (
    <center>
      {productId}{' '}
      <Formatted value={ticker.price} formatter="currency" />
    </center>
  );
}
interface Props {
  productId: string;
}
render(<AssetPrice productId="BTC-USD" />);

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Using HTTP Headers

HTTP Headers are accessible in the fetch Response. RestEndpoint.fetchResponse() can be used to construct RestEndpoint.

Sometimes this is used for cursor based pagination.

import { RestEndpoint, RestGenerics } from '@data-client/rest';

class GithubEndpoint<
  O extends RestGenerics = any,
> extends RestEndpoint<O> {
  async parseResponse(response: Response) {
    const results = await super.parseResponse(response);
    if (
      (response.headers && response.headers.has('link')) ||
      Array.isArray(results)
    ) {
      return {
        link: response.headers.get('link'),
        results,
      };
    }
    return results;
  }
}

Name calling

Sometimes an API might change a key name, or choose one you don't like. Of course you have much better naming standards, so instead of your Resource class definition and all your code, you just want to remap that key.

ArticleResource.ts
class RenamedEndpoint<
  O extends RestGenerics = any,
> extends RestEndpoint<O> {
  getRequestInit(body) {
    if (body && 'carrotsUsed' in body) {
      const newBody = {
        ...body,
        carrotsUSedIsThisNameTooLong: carrotsUsed,
      };
      delete newBody.carrotsUsed;
      return super.getRequestInit(newBody);
    }
    return super.getRequestInit(body);
  }
  process(value) {
    if ('carrotsUsedIsThisNameTooLong' in value) {
      // ok to mutate jsonResponse since we control it
      value.carrotsUsed = value.carrotsUsedIsThisNameTooLong;
      delete value.carrotsUsedIsThisNameTooLong;
    }
    return value;
  }
}

Snakes to camels​

Deserializing fields​

Deserializing Date​

Case of the missing Id​

Ticker prices​

Using HTTP Headers​

Name calling​