fast-fallback

Fast fallback Lib that supports P-cancelable.

Install

yarn add fast-fallback

//es6
import fallback from "fast-fallback";
 
//commonjs
const fallback = require("fast-fallback");

browser

<script src="https://unpkg.com/fast-fallback"></script>
<script>
 var fallback = fastFallback;
</script> 

Usage

Basic

const fallback = require("fast-fallback");
const PCancelable = require('promise-cancelable');
 
const servers = ['121.25.1.100', '121.25.1.101', '121.2.15.102']
 
const asyncTransformer = server => new PCancelable((resolve, reject, onCancel)=>{
  const ws = new WebSocket('ws://' + server)
 
  // Cancel late-successful connections.
  onCancel(_ => ws.close())
 
  ws.onopen = _ => resolve(ws)
  ws.onerror = err => reject(err)
});
 
(async_ => {
  const [ws] = await fallback(servers, asyncTransformer, {
    count: 1 // Number of fallback results
  })
 
  ws.send(...)
})()

Currying

const curried = fallback(asyncTransformer, opts) 
const results1 = await curried(servers)
const results2 = await curried(otherSevers)

API

fallback(values, asyncTransformer [, options])

values: array

Candidate values.

asyncTransformer: (val, idx) => PCancelable<Any>|Promise<Any>

Transform functions that generate promise using candidate value.

options: object

count

Number of fallback results. defaults 1.

concurrency

Number of concurrently processing promises. defaults Infinity.

silent

When all promises fail, return an empty array if true, or throw an exception if false. defaults false.

Related

• promise-cancelable - for browser
• p-cancelable - for node

License

MIT