@fine-js/channels/src/misc.js

Bits of Clojure's `core.async` ported to JS

'use strict'

const valueError = (val) => new TypeError(`Can not put \`${val}\` onto channel`)
const badval = (val) => val === null || val === undefined

const none = Symbol('none')
const once = (fn, multithrow = false) => {
  let cache = none

  return (...args) => {
    if (cache === none)
      cache = fn(...args)
    else if (multithrow === true)
      throw new Error(`${fn.name} called twice`)

    return cache
  }
}

// In node, we'd like to use setImmediate, but since browsers do not support it,
// we have to go with `setTimeout` of 0 milliseconds. We access `setImmediate`
// like we do, so that Browserify does not include its `timers` module.
const schedule = ((browser) => {
  return browser
    ? (fn, ...args) => void setTimeout(fn, 0, ...args)
    : global['set' + 'Immediate'] // eslint-disable-line  no-useless-concat
})(typeof window === 'object')

module.exports = {
  privates: Symbol('channels/private-apis'),
  badval,
  valueError,
  once,
  schedule,
}