Styled React component mixin with reference counting

gistfile1.js

function _mount(style, styles) {
  for (var i = 0; i < styles.length; i++) {
    if (style == styles[i].getAttribute('href')) {
      styles[i].dataset.refc++;
      return;
    }
  }

  var newStyle = document.createElement('link');
  newStyle.setAttribute('rel', 'stylesheet');
  newStyle.setAttribute('type', 'text/css');
  newStyle.setAttribute('href', style);
  newStyle.dataset.refc = 1;
  document.head.appendChild(newStyle);
}

function _unmount(style, styles) {
  var existingStyle;

  for (var i = 0; i < styles.length; i++) {
    if (style == styles[i].getAttribute('href')) {
      styles[i].dataset.refc--;
      existingStyle = styles[i];
      break;
    }
  }

  if (existingStyle.dataset.refc <= 0) {
    document.head.removeChild(existingStyle);
  }
}

var StyleMixin = {
  componentWillMount() {
    if (this.style) {
      var links = document.head.getElementsByTagName('link');
      var styles = [];

      for (var i = 0; i < links.length; i++) {
        if (links[i].getAttribute('rel') == 'stylesheet') {
          styles.push(links[i]);
        }
      }

      if (this.style.constructor === Array) {
        this.style.forEach(function (style) {
          _mount(style, styles);
        })
      }
      else {
        _mount(this.style, styles);
      }
    }
  },
  componentWillUnmount() {
    if (this.style) {
      var links = document.head.getElementsByTagName('link');
      var styles = [];

      for (var i = 0; i < links.length; i++) {
        if (links[i].getAttribute('rel') == 'stylesheet') {
          styles.push(links[i]);
        }
      }

      if (this.style.constructor === Array) {
        this.style.forEach(function (style) {
          _unmount(style, styles);
        })
      }
      else {
        _unmount(this.style, styles);
      }
    }
  }
}

export default StyleMixin;