caller.js

const handler = {
  get: (obj, prop) => {
    // Call should be run when calling invoke().
    if (prop === 'invoke') {
      return body => console.log(`Would call ${obj.route} with body: ${JSON.stringify(body)}`)
    }

    // First access sets the request method.
    if (obj.route === null) {
      return (new Proxy({ route: '', method: prop }, handler))
    }

    // Handle everything else.
    let newObj
    if (typeof prop !== 'symbol') {
      newObj = { ...obj, route: `${obj.route}/${prop}` }
    } else {
      newObj = { ...obj, route: obj.route }
    }
    return (new Proxy(newObj, handler))
  }
}

const api = new Proxy({ route: null }, handler)