code: function map(obj, cb, context) {
      if (!(obj && cb)) {
          return;
      }
      if (obj.map && obj.map === nativeMap) {
          return obj.map(cb, context);
      }
      else {
          var result = [];
          for (var i = 0, len = obj.length; i < len; i++) {
              result.push(cb.call(context, obj[i], i, obj));
          }
          return result;
      }
  }
docs: 数组或对象遍历
  @memberOf module:zrender/core/util
  @param {Object|Array} obj
  @param {Function} cb
  @param {*} [context]
   
  数组映射
  @memberOf module:zrender/core/util
  @param {Array} obj
  @param {Function} cb
  @param {*} [context]
  @return {Array}