React focus monitor mixin (click or focus outside of monitored node calls a handler)

FocusMonitorMixin.js

module.exports = {
  componentWillUnmount: function() {
    this.endFocusMonitor();
  },

  startFocusMonitor: function() {
    document.addEventListener('focusin', this.checkFocusTarget);
    document.addEventListener('click',   this.checkFocusTarget);
  },

  checkFocusTarget: function(event) {
    var element = event.target,
        monitoredNode = this.getFocusMonitoredNode();

    while (element) {
      if (element == monitoredNode) {
        break;
      }

      element = element.parentNode;
    }

    if (!element) {
      this.onFocusMonitoredNodeBlur();
    }
  },

  endFocusMonitor: function() {
    document.removeEventListener('focusin', this.checkFocusTarget)
    document.removeEventListener('click',   this.checkFocusTarget);
  }
}