wait-condition

Resolve a promise when a condition is met.

install

npm install wait-condition

usage

const waitCondition = require('wait-condition')
// or ES6
import waitCondition from 'wait-condition'

const condition = () => {
  if (somethingIsReady()) {
    return {
      done: true,
      value: someValue,
    }
  }
  return null
}

waitCondition(condition)
  .then((someValue) => { /* will be called when somethingIsReady() */ })
  .catch((reason) => { /* will be called whether the condition causes an error or after timeout */ })

options

// default values
waitCondition(condition, {
  initialInterval: 100, // milliseconds
  attemptsBeforeSlowing: 20,
  timeout: 60000, // milliseconds
})

how it works

short version

It starts checking the condition every initialInterval milliseconds. Every time attemptsBeforeSlowing attempts are reached, the interval is doubled, until timeout is reached.

long version

waitCondition receives a condition and returns a Promise. condition should be a function that returns falsy or an object like: { done: , value: , }

The condition is considered met when the done property is true.

Checks continuously for the condition and:

• resolves the Promise with the value property of condition result, if condition is met before timeout
• rejects the Promise if the condition is not met before timeout, or when an error occurs while evaluating the condition, and specifies the reason for rejection