REST JS proxy implementation based on https://gist.github.com/v1vendi/75d5e5dad7a2d1ef3fcb48234e4528cb

create-full-rest-proxy.js

const fetch = async (...args) => {
  console.log(...args)
  return { 
   statusCode: 200,
   data: {},
  }
}

function httpRequest(url, method, data, opts, cb) {
  const init = { method }
  switch (method) {
    case 'GET':
      if (data) {
        url = `${url}?${new URLSearchParams(data)}`
      }
      break
    case 'POST':
    case 'PUT':
    case 'PATCH':
      init.body = JSON.stringify(data)
  }

  // Run promise or callback
  return fetch(url, init).then((d) => {
    if (cb) return cb(undefined, d)
    return d
  }).catch((err) => {
    if (cb) return cb(err)
    throw err
  })
}

function generateAPI(url, scope = []) {
  // a hack, so we can use field either as property or a method
  const callable = () => {}
  callable.url = url

  return new Proxy(callable, {
    get({ url }, propKey) {
      const upperKey = propKey.toUpperCase()
      const prevScope = scope[scope.length - 1]
      const path = scope.concat(propKey)
      console.log('prevScope', prevScope)
      if (['GET', 'POST', 'PUT', 'DELETE', 'PATCH'].includes(upperKey)) {
        const resolvedPath = path.slice(0, -1)
        console.log('resolved SDK path', resolvedPath)

        const func = (data, options = {}, callback) => {
          console.log('data', data)
          console.log('options', options)
          const config = typeof options === 'function' ? {} : options
          const cb = typeof options === 'function' ? options : callback
          return httpRequest(url, upperKey, data, config, cb)
        }
        /* Add callable sub keys after HTTP method */
        func.sync = (data, options = {}) => {
          console.log('run sync thing', data)
          console.log('run sync opts', options)
        }
        /* Client signature */
        return func
      }
      return generateAPI(`${url}/${propKey}`, path)
    },
    apply({ url }, thisArg, [arg] = []) {
      // Mid chain function call ()
      // e.g. client.product(7).get()
      console.log('apply called', url)
      console.log('arg used', arg)
      const path = url.split('/')
      return generateAPI(arg ? `${url}/${arg}` : url, path)
    }
  })
}

/* Init client */
const client = generateAPI('https://base.com')
/* Usage example client.thing.xyz.operation() */
client.get()    // GET     https://base.com
client.post()   // PUT     https://base.com
client.put()    // POST    https://base.com
client.delete() // DELETE  https://base.com

const opts = { foo: 'bar' }

/* Mid chain calls with () work too but look weird */
// GET https://base.com/product/7
client.product(7).get() 
// GET with query strings https://base.com/base/tiles/public/static/2.json?turn=37038&games=wot
client.product(7).get({
  turn: 37,
  games: 'wot'
})
// DELETE https://base.com/product/7/whatever
client.product(7).whatever.delete(1, opts) 
// PUT with body https://base.com/product/7
client.product(7).put({ 
  whatever: 1
})
// POST with body https://base.com/product/7 w/ body
client.product(7).post({ 
  whatever: 1
})
// GET https://base.com/base/tiles/public/static/3/4/2.json
client.tiles.public.static(3)(4)(`${2}.json`).get()


/* Bracket syntax for numbers */
// GET https://base.com/product/7
client.product[7].get() 
// GET with query strings https://base.com/base/tiles/public/static/2.json?turn=37038&games=wot
client.product[7].get({
  turn: 37,
  games: 'wot'
})
// DELETE https://base.com/product/7/whatever
client.product[7].whatever.delete(1, opts) 
// PUT with body https://base.com/product/7
client.product[7].put({ 
  whatever: 1
})
// POST with body https://base.com/product/7
client.product[7].post({ 
  whatever: 1
})

/* Clean API */
// GET https://base.com/entities/product
client.entities.product.get() 
// GET with query strings https://base.com/entities/product?turn=37038&games=wot
client.entities.product.get({
  turn: 37,
  games: 'wot'
})
// DELETE https://base.com/entities/product
client.entities.product.delete(1, opts) 
// PUT with body https://base.com/entities/product
client.entities.product.put({ 
  whatever: 1
})
// POST with body https://base.com/entities/product
client.entities.product.post({ 
  whatever: 1
})

const payload = {
  foo: 'bar'
}
/* Callback Usage */
client.entity.shape[1].post(payload, (err, resp) => {
  console.log('callback', resp)
})

/* Promise Usage */
client.entity.shape.post(payload).then((resp) => {
  console.log('promise', resp)
})

/* Sync Usage */
client.entity.shape.post.sync(payload)