code: function cleanTables(font) {
              delete font.readOptions;
              delete font.tables;
              delete font.hmtx;
              delete font.post.glyphNameIndex;
              delete font.post.names;
              delete font.subsetMap;
  
              // 删除无用的表
              var cff = font.CFF;
              delete cff.glyf;
              delete cff.charset;
              delete cff.encoding;
              delete cff.gsubrs;
              delete cff.gsubrsBias;
              delete cff.subrs;
              delete cff.subrsBias;
          }
docs: 清除非必须的表
  @param {Object} font font对象