Eventually – Debounce for promises

eventually.js

'use strict';

var Promise = require('bluebird')

function eventually(callback, wait, leading) {
  var timer

  return function() {
    var context = this
    var args = arguments
    var resolve
    var called

    var promise = new Promise(function(deferred) {
      resolve = deferred
    }).then(function() {
      return callback.apply(context, args)
    })

    if (leading) {
      if (timer) {
        called = true
      } else {
        resolve()
      }
    }

    if (timer) {
      clearTimeout(timer)
    }

    timer = setTimeout(function() {
      timer = null

      if (!leading || called) {
        resolve()
      }
    }, wait)

    return promise
  }
}

module.exports = eventually