code: function getLegalBox(_ref) {
    var src = _ref.src,
        box = _ref.box;
  
    if (isString(box) && box) return box;
    src = src.toLowerCase();
    for (var key in boxSuffixMap) {
      var suffix = boxSuffixMap[key];
      if (src.indexOf(suffix) > -1) return key;
    }
    return 'native';
  }
docs: return the config box or choose the right one according to the src