fix: prevent crash when frames lack 3DMOL_STYLE blocks

src/GLModel.ts

@@ -1998,7 +1998,7 @@ export class GLModel {
             }
             model.molObj = null;
             if (model.modelDatas && framenum < model.modelDatas.length) {
-                model.modelData = model.modelDatas[framenum];
+                model.modelData = model.modelDatas[framenum] || {};
                 if (model.unitCellObjects && viewer) {
                     viewer.removeUnitCell(model);
                     viewer.addUnitCell(model);
@@ -2127,7 +2127,7 @@ export class GLModel {
         var mData = parsedAtoms.modelData;
         if (mData) {
             if (Array.isArray(mData)) {
-                this.modelData = mData[0];
+                this.modelData = mData[0] || {};
                 this.modelDatas = mData;
             } else {
                 this.modelData = mData;

src/parsers/SDF.ts

@@ -29,7 +29,8 @@ const apply3DmolStyle = function (
     return;
   }
 
-  const frameAtoms = atoms[atoms.length - 1];
+  const frameIdx = atoms.length - 1;
+  const frameAtoms = atoms[frameIdx];
 
   if (styleObj.bonds && typeof styleObj.bonds === "object") {
     const bonds = styleObj.bonds;
@@ -70,9 +71,6 @@ const apply3DmolStyle = function (
   }
 
   if (Object.keys(styleObj).length > 0) {
-    if (!atoms.modelData) atoms.modelData = [];
-    const frameIdx = atoms.length - 1;
-    if (!atoms.modelData[frameIdx]) atoms.modelData[frameIdx] = {};
     atoms.modelData[frameIdx].style = styleObj;
   }
 };
@@ -140,6 +138,8 @@ const addBond = function (curFrame: any[], from: number, to: number, order: numb
 
 const parseV2000 = function (lines: any, options: ParserOptionsSpec) {
   const atoms: any & Record<string, any> = [[]];
+  const modelData = atoms.modelData = [] as any[];
+  modelData.push({});  // entry for frame 0
   const noH = typeof options.keepH !== "undefined" ? !options.keepH : false;
   let lineIndex = 0;
 
@@ -192,7 +192,10 @@ const parseV2000 = function (lines: any, options: ParserOptionsSpec) {
     lineIndex = parseSDProperties(lines, lineIndex + offset, atoms, serialToIndex, start);
 
     if (!options.multimodel) break;
-    if (!options.onemol) atoms.push([]);
+    if (!options.onemol) {
+      atoms.push([]);
+      modelData.push({});  // 1:1 with frames — prevents undefined on frame switch
+    }
   }
   return atoms;
 };
@@ -205,6 +208,8 @@ const parseV2000 = function (lines: any, options: ParserOptionsSpec) {
 
 const parseV3000 = function (lines: any, options: ParserOptionsSpec) {
   const atoms: any[][] & Record<string, any> = [[]];
+  const modelData = atoms.modelData = [] as any[];
+  modelData.push({});  // entry for frame 0
   const noH = typeof options.keepH !== "undefined" ? !options.keepH : false;
   let lineIndex = 0;
 
@@ -280,7 +285,10 @@ const parseV3000 = function (lines: any, options: ParserOptionsSpec) {
     lineIndex = parseSDProperties(lines, lineIndex + offset, atoms, serialToIndex, start);
 
     if (!options.multimodel) break;
-    if (!options.onemol) atoms.push([]);
+    if (!options.onemol) {
+      atoms.push([]);
+      modelData.push({});  // 1:1 with frames
+    }
 
   }
   return atoms;

tests/parsers_tests/parsers-sdf.test.js

@@ -14,31 +14,41 @@ describe('Function SDF | parseV2000 |', ()=>{
     test("Atoms is empty when input data is not greater than 3 lines",()=>{
         let test_data1 = "line1\nline2\nline3";
         let test_atoms1 = $3Dmol.Parsers.SDF(test_data1, {});
-        expect(test_atoms1).toEqual([[]]);
+        expect(test_atoms1.length).toBe(1);
+        expect(test_atoms1[0]).toEqual([]);
+        expect(test_atoms1.modelData).toEqual([{}]);
     });
 
     test("Atoms is empty when length of line 4 of input data is less than 38",()=>{
         let test_data2 = "line1\nline2\nline3\nlessthan38";
         let test_atoms2 = $3Dmol.Parsers.SDF(test_data2, {});
-        expect(test_atoms2).toEqual([[]]);
+        expect(test_atoms2.length).toBe(1);
+        expect(test_atoms2[0]).toEqual([]);
+        expect(test_atoms2.modelData).toEqual([{}]);
     });
 
     test("Atoms is empty when atomCount is not a number", ()=>{
         let test_data3 = "line1\nline2\nline3\natomCount";
         let test_atoms3 = $3Dmol.Parsers.SDF(test_data3, {});
-        expect(test_atoms3).toEqual([[]]);
+        expect(test_atoms3.length).toBe(1);
+        expect(test_atoms3[0]).toEqual([]);
+        expect(test_atoms3.modelData).toEqual([{}]);
     });
 
     test("Atoms is empty when atomCount is not greater than 0", ()=>{
         let test_data4 = "line1\nline2\nline3\n -1";
         let test_atoms4 = $3Dmol.Parsers.SDF(test_data4, {});
-        expect(test_atoms4).toEqual([[]]);
+        expect(test_atoms4.length).toBe(1);
+        expect(test_atoms4[0]).toEqual([]);
+        expect(test_atoms4.modelData).toEqual([{}]);
     });
 
     test("Atoms is empty when the number of lines of input is less than 4 + atomCount + bondCount", ()=>{
         let test_data5 = "line1\nline2\nline3\n  1 0 ";// atomCount=0, bondCount=1
         let test_atoms5 = $3Dmol.Parsers.SDF(test_data5, {});
-        expect(test_atoms5).toEqual([[]]);
+        expect(test_atoms5.length).toBe(1);
+        expect(test_atoms5[0]).toEqual([]);
+        expect(test_atoms5.modelData).toEqual([{}]);
     });
 
     test("Length of atoms is 1", ()=>{