code: function getType(obj) {
    if (obj === null) return 'null';
    if (typeof obj === undefined) return 'undefined';
  
    return Object.prototype.toString.call(obj)
            .match(/\s([a-zA-Z]+)/)[1]
            .toLowerCase();
  }
docs: 获取传入参数类型
  @param  {String,Number,Array,Boolaen,Function,Object,Null,Undefined} obj
  @return {String}     []