spike out initial twoPass option for additional state retention.

src/idiomorph.js

@@ -201,6 +201,9 @@ var Idiomorph = (function () {
 
                 // innerHTML, so we are only updating the children
                 morphChildren(normalizedNewContent, oldNode, ctx);
+                if (ctx.twoPass) {
+                    restoreFromPantry(oldNode, ctx);
+                }
                 return Array.from(oldNode.children);
 
             } else if (ctx.morphStyle === "outerHTML" || ctx.morphStyle == null) {
@@ -713,11 +716,19 @@ var Idiomorph = (function () {
                 ignoreActiveValue: mergedConfig.ignoreActiveValue,
                 idMap: createIdMap(oldNode, newContent),
                 deadIds: new Set(),
+                pantry: mergedConfig.twoPass && createPantry(),
                 callbacks: mergedConfig.callbacks,
                 head: mergedConfig.head
             }
         }
 
+        function createPantry() {
+            const pantry = document.createElement("div");
+            pantry.hidden = true;
+            document.body.insertAdjacentHTML("afterend", pantry);
+            return pantry;
+        }
+
         /**
          *
          * @param {Node | null} node1
@@ -1063,11 +1074,49 @@ var Idiomorph = (function () {
         function removeNode(tempNode, ctx) {
             removeIdsFromConsideration(ctx, tempNode)
             if (ctx.callbacks.beforeNodeRemoved(tempNode) === false) return;
-
-            tempNode.parentNode?.removeChild(tempNode);
+            if (ctx.pantry) {
+                moveToPantry(tempNode.pantry, ctx);
+            } else {
+                tempNode.parentNode?.removeChild(tempNode);
+            }
             ctx.callbacks.afterNodeRemoved(tempNode);
         }
 
+        function moveToPantry(node, ctx) {
+            if (!node) return;
+
+            // If the node is a leaf (no children), process it, and then we're done
+            if (!node.children || node.children.length === 0) {
+                if (node.id) {
+                    ctx.pantry.appendChild(node);
+                }
+
+            // otherwise we need to process the children first
+            } else {
+                Array.from(node.children).forEach(child => {
+                    moveToPantry(child, ctx);
+                });
+
+                // After processing children, process the current node
+                if (node.id) {
+                    ctx.pantry.appendChild(node);
+                }
+            }
+        }
+
+        function restoreFromPantry(root, ctx) {
+            Array.from(ctx.pantry.children).forEach(element => {
+                const matchElement = root.findElementById(element.id);
+                if (matchElement) {
+                    matchElement.before(element);
+                    element.replaceChildren(matchElement.childNodes);
+                    matchElement.remove();
+                    syncNodeFrom(newContent, oldNode, ctx);
+                }
+            });
+            ctx.pantry.remove();
+        }
+
         //=============================================================================
         // ID Set Functions
         //=============================================================================

test/two-pass.js

@@ -0,0 +1,52 @@
+describe("Two-pass option for retaining more state", function(){
+
+    beforeEach(function() {
+        clearWorkArea();
+    });
+
+    it('fails to preserve all non-attribute element state with single-pass option', function()
+    {
+        getWorkArea().append(make(`
+            <div>
+              <input type="checkbox" checked id="first">
+              <input type="checkbox" checked id="second">
+            </div>
+        `));
+        document.getElementById("first").indeterminate = true
+        document.getElementById("second").indeterminate = true
+
+        let finalSrc = `
+            <div>
+              <input type="checkbox" checked id="second">
+              <input type="checkbox" checked id="first">
+            </div>
+        `;
+        Idiomorph.morph(getWorkArea(), finalSrc, {morphStyle:'innerHTML'});
+
+        document.getElementById("first").indeterminate.should.be.false
+        document.getElementById("second").indeterminate.should.be.true
+    });
+
+    it('preserves all non-attribute element state with two-pass option', function()
+    {
+        getWorkArea().append(make(`
+            <div>
+              <input type="checkbox" checked id="first">
+              <input type="checkbox" checked id="second">
+            </div>
+        `));
+        document.getElementById("first").indeterminate = true
+        document.getElementById("second").indeterminate = true
+
+        let finalSrc = `
+            <div>
+              <input type="checkbox" checked id="second">
+              <input type="checkbox" checked id="first">
+            </div>
+        `;
+        Idiomorph.morph(getWorkArea(), finalSrc, {morphStyle:'innerHTML',twoPass:true});
+
+        document.getElementById("first").indeterminate.should.be.true
+        document.getElementById("second").indeterminate.should.be.true
+    });
+});