From 63f4fb10a508f08fe99efdc66127121a64d9c9e1 Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 13:14:49 +0100
Subject: [PATCH 01/11] [rntuple] first std::bitset implementation

---
 modules/rntuple.mjs | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/modules/rntuple.mjs b/modules/rntuple.mjs
index bc85d8d66..d4fd9b1d1 100644
--- a/modules/rntuple.mjs
+++ b/modules/rntuple.mjs
@@ -1132,6 +1132,38 @@ class ArrayReaderItem extends ReaderItem {
 }
 
 
+/** @class reading of std::bitset<N>
+ * @desc large numbers with more than 48 bits converted to BigInt
+ * @private */
+
+class BitsetReaderItem extends ReaderItem {
+
+   constructor(items, tgtname, size) {
+      super(items, tgtname);
+      this.size = size;
+      items[0].set_not_simple();
+      this.bigint = size > 48;
+   }
+
+   func(tgtobj) {
+      const tmp = {};
+      let len = 0, res = 0;
+      while (len < this.size) {
+         this.items[0].func(tmp);
+         if (tmp.bit)
+            res |= 1 << len;
+         len++;
+      }
+      tgtobj[this.name] = res;
+   }
+
+   shift(entries) {
+      this.items[0].shift(entries * this.size);
+   }
+
+}
+
+
 /** @class reading std::vector and other kinds of collections
  * @private */
 
@@ -1370,6 +1402,12 @@ async function rntupleProcess(rntuple, selector, args = {}) {
          return new StringReaderItem([itemlen, itemstr], tgtname);
       }
 
+      if ((columns.length === 1) && (field.typeName.indexOf('std::bitset') === 0)) {
+         const itembit = addColumnReadout(columns[0], 'bit');
+         return new BitsetReaderItem([itembit], tgtname, Number(field.arraySize));
+      }
+
+
       let is_stl = false;
       ['vector', 'map', 'unordered_map', 'multimap', 'unordered_multimap', 'set', 'unordered_set', 'multiset', 'unordered_multiset'].forEach(name => {
          if (field.typeName.indexOf('std::' + name) === 0)

From e9e48275e38a0349958beae7b883387d38d4d70c Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 13:25:40 +0100
Subject: [PATCH 02/11] [rntuple] check for normal bitset

---
 demo/node/rntuple_test.js | 68 +++++++++++++++++++++------------------
 1 file changed, 37 insertions(+), 31 deletions(-)

diff --git a/demo/node/rntuple_test.js b/demo/node/rntuple_test.js
index fbc05f35f..ab1575d4e 100644
--- a/demo/node/rntuple_test.js
+++ b/demo/node/rntuple_test.js
@@ -5,73 +5,79 @@ import { readHeaderFooter, rntupleProcess } from 'jsroot/rntuple';
 console.log(`JSROOT version ${version}`);
 
 
-let filename = './rntuple_test.root';
+let filename = './rntuple_test.root',
+    any_error = false;
+
 if (process?.argv && process.argv[2])
    filename = process.argv[2];
 
 const file = await openFile(filename),
-      rntuple = await file.readObject('Data');
-
-await readHeaderFooter(rntuple);
+      rntuple = await file.readObject('Data'),
+      builder = await readHeaderFooter(rntuple);
 
 console.log('Performing Validations and debugging info');
 
-if (rntuple.builder?.name !== 'Data')
+if (builder?.name !== 'Data')
    console.error('FAILURE: name differs from expected');
 else
-   console.log('OK: name is', rntuple.builder?.name);
+   console.log('OK: name is', builder?.name);
 
 
-if (rntuple.builder?.description !== '')
+if (builder.description !== '')
    console.error('FAILURE: description should be the empty string');
 else
    console.log('OK: description is empty string');
 
-if (rntuple.builder?.xxhash3 === undefined || rntuple.builder.xxhash3 === null)
+if (builder.xxhash3 === undefined || builder.xxhash3 === null)
    console.warn('WARNING: xxhash3 is missing');
 else
-   console.log('OK: xxhash3 is', '0x' + rntuple.builder.xxhash3.toString(16).padStart(16, '0'));
+   console.log('OK: xxhash3 is', '0x' + builder.xxhash3.toString(16).padStart(16, '0'));
 
 // Fields Check
 
-if (!rntuple.builder?.fieldDescriptors?.length)
+if (!builder?.fieldDescriptors?.length)
    console.error('FAILURE: No fields deserialized');
 else {
-   console.log(`OK: ${rntuple.builder.fieldDescriptors.length} field(s) deserialized`);
-   for (let i = 0; i < rntuple.builder.fieldDescriptors.length; ++i) {
-      const field = rntuple.builder.fieldDescriptors[i];
+   console.log(`OK: ${builder.fieldDescriptors.length} field(s) deserialized`);
+   for (let i = 0; i < builder.fieldDescriptors.length; ++i) {
+      const field = builder.fieldDescriptors[i];
       if (!field.fieldName || !field.typeName)
          console.error(`FAILURE: Field ${i} is missing name or type`);
       else
          console.log(`OK: Field ${i}: ${field.fieldName} (${field.typeName})`);
       if (i === 0) {
-         if (field.fieldName !== 'IntField' || field.typeName !== 'std::int32_t')
+         if (field.fieldName !== 'IntField' || field.typeName !== 'std::int32_t') {
+            any_error = true;
             console.error(`FAILURE: First field should be 'IntField (std::int32_t)' but got '${field.fieldName} (${field.typeName})'`);
-      } else if (i === rntuple.builder.fieldDescriptors.length - 1) {
-         if (field.fieldName !== '_1' || field.typeName !== 'bool')
+         }
+      } else if (i === builder.fieldDescriptors.length - 1) {
+         if (field.fieldName !== '_1' || field.typeName !== 'bool') {
+            any_error = true;
             console.error(`FAILURE: Last field should be '_1 (bool)' but got '${field.fieldName} (${field.typeName})'`);
+         }
       }
    }
 }
 
 // Column Check
 
-if (!rntuple.builder?.columnDescriptors?.length)
+if (!rntuple.builder?.columnDescriptors?.length) {
+   any_error = true;
    console.error('FAILURE: No columns deserialized');
-else {
-   console.log(`OK: ${rntuple.builder.columnDescriptors.length} column(s) deserialized`);
-   for (let i = 0; i < rntuple.builder.columnDescriptors.length; ++i) {
-      const column = rntuple.builder.columnDescriptors[i];
+} else {
+   console.log(`OK: ${builder.columnDescriptors.length} column(s) deserialized`);
+   for (let i = 0; i < builder.columnDescriptors.length; ++i) {
+      const column = builder.columnDescriptors[i];
       if (column.fieldId === undefined || column.fieldId === null)
          console.error(`FAILURE: Column ${i} is missing fieldId`);
       else
          console.log(`OK: Column ${i} fieldId: ${column.fieldId} `);
-      if (i === 0) {
-         if (column.fieldId !== 0)
-            console.error('FAILURE: First column should be for fieldId 0');
-      } else if (i === rntuple.builder.columnDescriptors.length - 1) {
-         if (column.fieldId !== 38)
-            console.error('FAILURE: Last column should be for fieldId 38');
+      if ((i === 0) && (column.fieldId !== 0)) {
+         any_error = true;
+         console.error('FAILURE: First column should be for fieldId 0');
+      } else if ((i === builder.columnDescriptors.length - 1) && (column.fieldId !== builder.fieldDescriptors.length - 1)) {
+         any_error = true;
+         console.error(`FAILURE: Last column should be for fieldId ${builder.fieldDescriptors.length - 1}`);
       }
    }
 }
@@ -81,9 +87,10 @@ const selector = new TSelector(),
       fields = ['IntField', 'FloatField', 'DoubleField',
                 'Float16Field', 'Real32Trunc', 'Real32Quant',
                 'StringField', 'BoolField',
+                'BitsetField',
                 'ArrayInt', 'VariantField', 'TupleField',
                 'VectString', 'VectInt', 'VectBool', 'Vect2Float', 'Vect2Bool', 'MultisetField',
-                'MapStringFloat', 'MapIntDouble', 'MapStringBool'],
+                'MapStringFloat', 'MapIntDouble', 'MapStringBool' ],
       epsilonValues = { Real32Trunc: 0.3, Real32Quant: 1e-4, Float16Field: 1e-2 };
 
 for (const f of fields)
@@ -97,8 +104,6 @@ selector.Begin = () => {
 // Now validate entry data
 const EPSILON = 1e-7;
 
-let any_error = false;
-
 function compare(expected, value, eps) {
    if (typeof expected === 'number')
       return Math.abs(value - expected) < (eps ?? EPSILON);
@@ -144,7 +149,8 @@ selector.Process = function(entryIndex) {
       MultisetField: [],
       MapStringFloat: [],
       MapIntDouble: [],
-      MapStringBool: []
+      MapStringBool: [],
+      BitsetField: 1 << entryIndex * 3 % 25
    }, npx = (entryIndex + 5) % 7;
 
    switch (entryIndex % 3) {

From da9b4fe542265dbd1fdc3e12190eaf4cb167b731 Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 13:37:52 +0100
Subject: [PATCH 03/11] [rntuple] read large bitset as BigInt

---
 modules/rntuple.mjs | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/modules/rntuple.mjs b/modules/rntuple.mjs
index d4fd9b1d1..917ced099 100644
--- a/modules/rntuple.mjs
+++ b/modules/rntuple.mjs
@@ -1147,11 +1147,15 @@ class BitsetReaderItem extends ReaderItem {
 
    func(tgtobj) {
       const tmp = {};
-      let len = 0, res = 0;
+      let len = 0, res = this.bigint ? 0n : 0;
       while (len < this.size) {
          this.items[0].func(tmp);
-         if (tmp.bit)
-            res |= 1 << len;
+         if (tmp.bit) {
+            if (this.bigint)
+               res |= (1n << BigInt(len));
+            else
+               res |= 1 << len;
+         }
          len++;
       }
       tgtobj[this.name] = res;

From 92b91d1c5c4ecad7189486e39b0e91d1372e5ed4 Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 13:38:06 +0100
Subject: [PATCH 04/11] [rntuple] add testing of large bitset

---
 demo/node/rntuple_test.cxx | 13 +++++++++++++
 demo/node/rntuple_test.js  | 14 ++++++++------
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/demo/node/rntuple_test.cxx b/demo/node/rntuple_test.cxx
index cdb3253b0..1350ecb1e 100644
--- a/demo/node/rntuple_test.cxx
+++ b/demo/node/rntuple_test.cxx
@@ -13,6 +13,7 @@
 #include <tuple>
 #include <map>
 #include <set>
+#include <bitset>
 
 #ifdef __ROOTCLING__
 #pragma link C++ class std::map<std::string,float>+;
@@ -21,6 +22,8 @@
 #pragma link C++ class std::multiset<std::string>+;
 #pragma link C++ class std::variant<std::string,int,bool>+;
 #pragma link C++ class std::tuple<std::string,int,bool>+;
+#pragma link C++ class std::bitset<25>+;
+#pragma link C++ class std::bitset<117>+;
 #endif
 
 
@@ -55,6 +58,8 @@ void rntuple_test()
    auto VariantField = model->MakeField<std::variant<std::string,int,bool>>("VariantField");
    auto TupleField = model->MakeField<std::tuple<std::string,int,bool>>("TupleField");
    auto ArrayInt = model->MakeField<std::array<int,5>>("ArrayInt");
+   auto BitsetField = model->MakeField<std::bitset<25>>("BitsetField");
+   auto LargeBitsetField = model->MakeField<std::bitset<117>>("LargeBitsetField");
    auto VectString   = model->MakeField<std::vector<std::string>>("VectString");
    auto VectInt   = model->MakeField<std::vector<int>>("VectInt");
    auto VectBool   = model->MakeField<std::vector<bool>>("VectBool");
@@ -103,6 +108,14 @@ void rntuple_test()
       Vect2Float->clear();
       Vect2Bool->clear();
 
+      BitsetField->reset();
+      LargeBitsetField->reset();
+
+      BitsetField->set(i * 3 % 25, true);
+
+      LargeBitsetField->set((i + 7) % 117, true);
+      LargeBitsetField->set((i + 35) % 117, true);
+
       int npx = (i + 5) % 7;
       for (int j = 0; j < npx; ++j) {
          VectString->emplace_back("str_" + std::to_string(j));
diff --git a/demo/node/rntuple_test.js b/demo/node/rntuple_test.js
index ab1575d4e..0276b2cff 100644
--- a/demo/node/rntuple_test.js
+++ b/demo/node/rntuple_test.js
@@ -87,8 +87,7 @@ const selector = new TSelector(),
       fields = ['IntField', 'FloatField', 'DoubleField',
                 'Float16Field', 'Real32Trunc', 'Real32Quant',
                 'StringField', 'BoolField',
-                'BitsetField',
-                'ArrayInt', 'VariantField', 'TupleField',
+                'ArrayInt', 'BitsetField', 'LargeBitsetField', 'VariantField', 'TupleField',
                 'VectString', 'VectInt', 'VectBool', 'Vect2Float', 'Vect2Bool', 'MultisetField',
                 'MapStringFloat', 'MapIntDouble', 'MapStringBool' ],
       epsilonValues = { Real32Trunc: 0.3, Real32Quant: 1e-4, Float16Field: 1e-2 };
@@ -139,6 +138,8 @@ selector.Process = function(entryIndex) {
       StringField: `entry_${entryIndex}`,
       BoolField: entryIndex % 3 === 1,
       ArrayInt: [entryIndex + 1, entryIndex + 2, entryIndex + 3, entryIndex + 4, entryIndex + 5],
+      BitsetField: 1 << entryIndex * 3 % 25,
+      LargeBitsetField: (1n << BigInt((entryIndex + 7) % 117)) | (1n << BigInt((entryIndex + 35) % 117)),
       VariantField: null,
       TupleField: { _0: `tuple_${entryIndex}`, _1: entryIndex*3, _2: (entryIndex % 3 === 1) },
       VectString: [],
@@ -149,8 +150,7 @@ selector.Process = function(entryIndex) {
       MultisetField: [],
       MapStringFloat: [],
       MapIntDouble: [],
-      MapStringBool: [],
-      BitsetField: 1 << entryIndex * 3 % 25
+      MapStringBool: []
    }, npx = (entryIndex + 5) % 7;
 
    switch (entryIndex % 3) {
@@ -189,8 +189,10 @@ selector.Process = function(entryIndex) {
          if (!compare(expected, value, epsilonValues[field])) {
             console.error(`FAILURE: ${field} at entry ${entryIndex} expected ${JSON.stringify(expected)}, got ${JSON.stringify(value)}`);
             any_error = true;
-         } else
-            console.log(`OK: ${field} at entry ${entryIndex} = ${JSON.stringify(value)}`);
+         } else {
+            const res = typeof value === 'bigint' ? value.toString() + 'n' : JSON.stringify(value);
+            console.log(`OK: ${field} at entry ${entryIndex} = ${res}`);
+         }
       } catch (err) {
          console.error(`ERROR: Failed to read ${field} at entry ${entryIndex}: ${err.message}`);
          any_error = true;

From dd911f16b475538155edbc7534833255b602f8aa Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 13:42:17 +0100
Subject: [PATCH 05/11] Extra mark BigInt value in hpainter

---
 modules/gui/HierarchyPainter.mjs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/modules/gui/HierarchyPainter.mjs b/modules/gui/HierarchyPainter.mjs
index 49c8e88c6..a76a4f06d 100644
--- a/modules/gui/HierarchyPainter.mjs
+++ b/modules/gui/HierarchyPainter.mjs
@@ -558,7 +558,11 @@ function objectHierarchy(top, obj, args = undefined) {
                }
             }
          }
-      } else if ((typeof fld === 'number') || (typeof fld === 'boolean') || (typeof fld === 'bigint')) {
+      } else if (typeof fld === 'bigint') {
+         simple = true;
+         item._value = fld.toString() + 'n';
+         item._vclass = cssValueNum;
+      } else if ((typeof fld === 'number') || (typeof fld === 'boolean')) {
          simple = true;
          if (key === 'fBits')
             item._value = '0x' + fld.toString(16);

From db23dc257e698ef81fae2a21bd98a288c9e231d7 Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 13:56:00 +0100
Subject: [PATCH 06/11] [rntuple] add atomic support

---
 modules/rntuple.mjs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/modules/rntuple.mjs b/modules/rntuple.mjs
index 917ced099..6b01f7884 100644
--- a/modules/rntuple.mjs
+++ b/modules/rntuple.mjs
@@ -1390,6 +1390,10 @@ async function rntupleProcess(rntuple, selector, args = {}) {
             return new ArrayReaderItem([item1], tgtname, Number(field.arraySize));
          }
 
+         if ((childs.length === 1) && (field.typeName.indexOf('std::atomic') === 0))
+            return addFieldReading(builder, childs[0], tgtname);
+
+
          if ((childs.length > 0) && (field.typeName.indexOf('std::tuple') === 0)) {
             const items = [];
             for (let i = 0; i < childs.length; ++i)

From e2c17d87a46aeffa1e096c6902c61ac27091b05a Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 13:56:23 +0100
Subject: [PATCH 07/11] [rntuple] add atomic testing

---
 demo/node/rntuple_test.cxx | 3 +++
 demo/node/rntuple_test.js  | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/demo/node/rntuple_test.cxx b/demo/node/rntuple_test.cxx
index 1350ecb1e..4a258013b 100644
--- a/demo/node/rntuple_test.cxx
+++ b/demo/node/rntuple_test.cxx
@@ -60,6 +60,7 @@ void rntuple_test()
    auto ArrayInt = model->MakeField<std::array<int,5>>("ArrayInt");
    auto BitsetField = model->MakeField<std::bitset<25>>("BitsetField");
    auto LargeBitsetField = model->MakeField<std::bitset<117>>("LargeBitsetField");
+   auto AtomicDoubleField = model->MakeField<std::atomic<double>>("AtomicDoubleField");
    auto VectString   = model->MakeField<std::vector<std::string>>("VectString");
    auto VectInt   = model->MakeField<std::vector<int>>("VectInt");
    auto VectBool   = model->MakeField<std::vector<bool>>("VectBool");
@@ -116,6 +117,8 @@ void rntuple_test()
       LargeBitsetField->set((i + 7) % 117, true);
       LargeBitsetField->set((i + 35) % 117, true);
 
+      *AtomicDoubleField = 111.444 * i;
+
       int npx = (i + 5) % 7;
       for (int j = 0; j < npx; ++j) {
          VectString->emplace_back("str_" + std::to_string(j));
diff --git a/demo/node/rntuple_test.js b/demo/node/rntuple_test.js
index 0276b2cff..519875ca6 100644
--- a/demo/node/rntuple_test.js
+++ b/demo/node/rntuple_test.js
@@ -87,7 +87,8 @@ const selector = new TSelector(),
       fields = ['IntField', 'FloatField', 'DoubleField',
                 'Float16Field', 'Real32Trunc', 'Real32Quant',
                 'StringField', 'BoolField',
-                'ArrayInt', 'BitsetField', 'LargeBitsetField', 'VariantField', 'TupleField',
+                'ArrayInt', 'BitsetField', 'LargeBitsetField',
+                'AtomicDoubleField', 'VariantField', 'TupleField',
                 'VectString', 'VectInt', 'VectBool', 'Vect2Float', 'Vect2Bool', 'MultisetField',
                 'MapStringFloat', 'MapIntDouble', 'MapStringBool' ],
       epsilonValues = { Real32Trunc: 0.3, Real32Quant: 1e-4, Float16Field: 1e-2 };
@@ -140,6 +141,7 @@ selector.Process = function(entryIndex) {
       ArrayInt: [entryIndex + 1, entryIndex + 2, entryIndex + 3, entryIndex + 4, entryIndex + 5],
       BitsetField: 1 << entryIndex * 3 % 25,
       LargeBitsetField: (1n << BigInt((entryIndex + 7) % 117)) | (1n << BigInt((entryIndex + 35) % 117)),
+      AtomicDoubleField: entryIndex * 111.444,
       VariantField: null,
       TupleField: { _0: `tuple_${entryIndex}`, _1: entryIndex*3, _2: (entryIndex % 3 === 1) },
       VectString: [],

From 5ef506ac68bcbd5ec93e24d21b52c176cee6af7c Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 14:13:28 +0100
Subject: [PATCH 08/11] [rntuple] support custom class field

For now only simple case
---
 modules/rntuple.mjs | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/modules/rntuple.mjs b/modules/rntuple.mjs
index 6b01f7884..dc61a7ee3 100644
--- a/modules/rntuple.mjs
+++ b/modules/rntuple.mjs
@@ -1215,7 +1215,6 @@ class VariantReaderItem extends ReaderItem {
 
    constructor(items, tgtname) {
       super(items, tgtname);
-      this.items = items;
       this.set_not_simple();
    }
 
@@ -1249,6 +1248,31 @@ class TupleReaderItem extends ReaderItem {
 
 }
 
+/** @class reading std::tuple<> field
+  * @private */
+
+class CustomClassReaderItem extends ReaderItem {
+
+   constructor(items, tgtname, classname) {
+      super(items, tgtname);
+      this.classname = classname;
+      this.set_not_simple();
+   }
+
+   func(tgtobj) {
+      const obj = { _typename: this.classname };
+      this.items.forEach(item => item.func(obj));
+      tgtobj[this.name] = obj;
+   }
+
+   shift(entries) {
+      this.items.forEach(item => item.shift(entries));
+   }
+
+}
+
+
+
 
 /** @class reading std::pair field
  * @private */
@@ -1401,6 +1425,13 @@ async function rntupleProcess(rntuple, selector, args = {}) {
             return new TupleReaderItem(items, tgtname);
          }
 
+         if ((childs.length > 0) && field.checksum && field.typeName) {
+            const items = [];
+            for (let i = 0; i < childs.length; ++i)
+               items.push(addFieldReading(builder, childs[i], childs[i].fieldName));
+            return new CustomClassReaderItem(items, tgtname, field.typeName);
+         }
+
          throw new Error(`No columns found for field '${field.fieldName}' in RNTuple`);
       }
 

From 1ef2f2a1c52a5cf3cf5ac4d4042f28824ffb638c Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 14:16:07 +0100
Subject: [PATCH 09/11] [rntuple] add testing of custom class

Include updated reference file
---
 demo/node/rntuple_test.cxx  |  14 ++++++++++++++
 demo/node/rntuple_test.js   |   3 ++-
 demo/node/rntuple_test.root | Bin 3895 -> 4610 bytes
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/demo/node/rntuple_test.cxx b/demo/node/rntuple_test.cxx
index 4a258013b..cad46b363 100644
--- a/demo/node/rntuple_test.cxx
+++ b/demo/node/rntuple_test.cxx
@@ -15,6 +15,14 @@
 #include <set>
 #include <bitset>
 
+class TestClass {
+   public:
+      std::string fName;
+      std::string fTitle;
+      double fValue{0.};
+
+};
+
 #ifdef __ROOTCLING__
 #pragma link C++ class std::map<std::string,float>+;
 #pragma link C++ class std::map<int,double>+;
@@ -24,6 +32,7 @@
 #pragma link C++ class std::tuple<std::string,int,bool>+;
 #pragma link C++ class std::bitset<25>+;
 #pragma link C++ class std::bitset<117>+;
+#pragma link C++ class TestClass+;
 #endif
 
 
@@ -61,6 +70,7 @@ void rntuple_test()
    auto BitsetField = model->MakeField<std::bitset<25>>("BitsetField");
    auto LargeBitsetField = model->MakeField<std::bitset<117>>("LargeBitsetField");
    auto AtomicDoubleField = model->MakeField<std::atomic<double>>("AtomicDoubleField");
+   auto TestClassField = model->MakeField<TestClass>("TestClassField");
    auto VectString   = model->MakeField<std::vector<std::string>>("VectString");
    auto VectInt   = model->MakeField<std::vector<int>>("VectInt");
    auto VectBool   = model->MakeField<std::vector<bool>>("VectBool");
@@ -96,6 +106,10 @@ void rntuple_test()
 
       *TupleField = { std::string("tuple_") + std::to_string(i), i * 3, (i % 3 == 1) };
 
+      TestClassField->fName = "name_" + std::to_string(i);
+      TestClassField->fTitle = "title_" + std::to_string(i);
+      TestClassField->fValue = i;
+
       VectString->clear();
       VectInt->clear();
       VectBool->clear();
diff --git a/demo/node/rntuple_test.js b/demo/node/rntuple_test.js
index 519875ca6..5442eaeec 100644
--- a/demo/node/rntuple_test.js
+++ b/demo/node/rntuple_test.js
@@ -88,7 +88,7 @@ const selector = new TSelector(),
                 'Float16Field', 'Real32Trunc', 'Real32Quant',
                 'StringField', 'BoolField',
                 'ArrayInt', 'BitsetField', 'LargeBitsetField',
-                'AtomicDoubleField', 'VariantField', 'TupleField',
+                'AtomicDoubleField', 'TestClassField', 'VariantField', 'TupleField',
                 'VectString', 'VectInt', 'VectBool', 'Vect2Float', 'Vect2Bool', 'MultisetField',
                 'MapStringFloat', 'MapIntDouble', 'MapStringBool' ],
       epsilonValues = { Real32Trunc: 0.3, Real32Quant: 1e-4, Float16Field: 1e-2 };
@@ -142,6 +142,7 @@ selector.Process = function(entryIndex) {
       BitsetField: 1 << entryIndex * 3 % 25,
       LargeBitsetField: (1n << BigInt((entryIndex + 7) % 117)) | (1n << BigInt((entryIndex + 35) % 117)),
       AtomicDoubleField: entryIndex * 111.444,
+      TestClassField: { _typename: 'TestClass', fName: `name_${entryIndex}`, fTitle: `title_${entryIndex}`, fValue: entryIndex },
       VariantField: null,
       TupleField: { _0: `tuple_${entryIndex}`, _1: entryIndex*3, _2: (entryIndex % 3 === 1) },
       VectString: [],
diff --git a/demo/node/rntuple_test.root b/demo/node/rntuple_test.root
index a610d96d8476167f25fbe1084da800757763a8a8..9c576ecffdf4fc8e9970a32fa18de2c88bafa12b 100644
GIT binary patch
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From f02f13d046825e2f34d670dab8f1144c55245f0f Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 14:18:08 +0100
Subject: [PATCH 10/11] Update comment

---
 changes.md          | 5 ++++-
 modules/rntuple.mjs | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/changes.md b/changes.md
index 31d666a98..4fbc1f077 100644
--- a/changes.md
+++ b/changes.md
@@ -3,13 +3,16 @@
 
 ## Changes in dev
 1. Implement new data types in `RNtuple`
+   - reduced float types kFloat16, kReal32Trunc, kReal32Quant
    - `std::vector`
    - `std::map`, `std::unordered_map`, `std::multimap`, `std::unordered_multimap` with `std::pair`
    - `std::set`, `std::unordered_set`, `std::multiset`, `std::unordered_multiset`
    - `std::array`
    - `std::variant`
    - `std::tuple`
-   - kFloat16, kReal32Trunc, kReal32Quant
+   - `std::bitset`
+   - `std::atomic`
+   - simple custom classes
 1. Resort order of ranges in http request, fixing several long-standing problems #374
 1. Implement for `TPie` 3d, text, title drawing including interactivity
 1. Implement `TCanvas` support in `build3d` function #373
diff --git a/modules/rntuple.mjs b/modules/rntuple.mjs
index dc61a7ee3..65dbbdcd1 100644
--- a/modules/rntuple.mjs
+++ b/modules/rntuple.mjs
@@ -1248,7 +1248,7 @@ class TupleReaderItem extends ReaderItem {
 
 }
 
-/** @class reading std::tuple<> field
+/** @class reading custom class field
   * @private */
 
 class CustomClassReaderItem extends ReaderItem {

From 5c13465f88b3b5c28f8e684599dbbe43c9cca9c3 Mon Sep 17 00:00:00 2001
From: Sergey Linev <S.Linev@gsi.de>
Date: Thu, 19 Feb 2026 14:21:46 +0100
Subject: [PATCH 11/11] Fix eslint warning

---
 modules/rntuple.mjs | 2 --
 1 file changed, 2 deletions(-)

diff --git a/modules/rntuple.mjs b/modules/rntuple.mjs
index 65dbbdcd1..4e73fa164 100644
--- a/modules/rntuple.mjs
+++ b/modules/rntuple.mjs
@@ -1272,8 +1272,6 @@ class CustomClassReaderItem extends ReaderItem {
 }
 
 
-
-
 /** @class reading std::pair field
  * @private */