onTransitionEnd one-off function

mixin.js

var transitionend = require('transitionend-property')

module.exports = {
  onTransitionEnd: function(el, fn) {
    var self = this
    function handler(event) {
      fn.call(self, event)
      el.removeEventListener(event.type, handler)
    }
    el.addEventListener(transitionend, handler, false)
  }
}