resolve-fetch-synchronously.js

const resolveSynchronously = promises => {
  if (promises.length > 0) {
    const [next, resolve] = promises[0]
    next.then(value => {
      resolve(value)
      // shift must be performed here to avoid accidentally creating a situation where
      // pendingUpdates length === 1, allowing for subsequent requests to potentially
      // resolve first
      promises.shift()
      resolveSynchronously(promises)
    })
  }
}

const createFetchContext = () => {
  const pendingUpdates = []
  
  return (url, opt) => new Promise(resolve => {
    pendingUpdates.push([fetch(url, opt), resolve])
    // if this is the only pending query, go ahead and resolve it
    if (pendingUpdates.length === 1) {
      resolveSynchronously(pendingUpdates)
    }
  })
}

// usage
const fetchSync = createFetchContext()
// these will resolve synchronously
fetchSync('https://jsonplaceholder.typicode.com/todos/1').then(r => console.log('Resolved 1', r))
fetchSync('https://jsonplaceholder.typicode.com/todos/2').then(r => console.log('Resolved 2', r))