Rewait

A NodeJS library to wait for external resources to become available:

• files
• sockets
• http/https
• custom functions

For example, you may wish to wait for a database or message queue to become available before starting your HTTP server. Rewait does that.

Install

Easily install with the following NPM command, or download a release.

npm i rewait

Why use rewait?

• No dependencies
• Tiny (~400 logical lines of code)
• 100% test coverage
• Permissive FOSS license
• Written in TypeScript
• Used in major production evironments
• Extensible

Usage

For detailed usage info, see the API documentation here.

Example

See more examples here.

const { retry, http, socket } = require('rewait')

retry(
  [
    http('http://localhost:3000'),
    http('https://localhost:3001/path/to/thing.txt'),
    socket('/var/run/app.sock'),
  ],
  {
    interval: 250, // check (at most) every 1/4 second
    timeout: 60000, // timeout after 60 seconds (on the dot)
  }
).then(() => {
  console.log('Ready!')
})

Custom checks

If you need custom functionality, you can easily write your own custom checks.

Simply throw an Error when "not ready".

Example:

function customCheck(options = {}) {
  return new Promise(function() {
    if (options.neverReady) {
      throw new Error('Never ready!')
    }
    if (options.waitUntil) {
      if (+new Date() < options.waitUntil) {
        throw new Error('Not ready!')
      }
    }
    // Ready, simply by not throwing
  })
}