/**

 * 滚动到index

 * @param option = {

 *  parentsDom //父元素 dom

 *  childDom   //子元素 dom

 * }

 */

Vue.prototype.scrollToIndex = function (options = {}) {

  let width = 0;
  // 在全局找到

  const el = document.getElementsByClassName(options.parentsDom),

    defaults = setDefault(options),

    elChild = document.getElementsByClassName(options.childDom);

  if (!judgeOptions(defaults)) {

    return;

  }

  if (defaults.x) {

    width = elChild[0].offsetLeft;

  }

  scrollLeft(el, width);

};

function setDefault(options) {

  const defaults = {

    parentsDom: '',

    childDom: '',

    x: true,

    y: false,

  };

  return Object.assign({}, defaults, options);

}

function judgeOptions(options) {

  console.log(options, 'options');

  if (typeof options.parentsDom !== 'string' || typeof options.childDom !== 'string'

    || document.getElementsByClassName(options.parentsDom).length === 0

    || document.getElementsByClassName(options.childDom).length === 0

  ) {

    console.warn('Dom必须传是className并且存在');

    return false;

  }

  return true;

}

function scrollLeft(el = '', width = 0) {

  if (!el) {

    return;

  }

  el[0].scrollLeft = width;

}

this.scrollToIndex({

    parentsDom: 'J-nav-select',

    childDom: 'J-nav-active',

});