improve id matching during findBestMatch

src/idiomorph.js

@@ -384,6 +384,10 @@ var Idiomorph = (function () {
         let softMatch = null;
         let nextSibling = node.nextSibling;
         let siblingSoftMatchCount = 0;
+        let displaceMatchCount = 0;
+
+        // max id matches we are willing to displace in our search
+        const nodeMatchCount = ctx.idMap.get(node)?.size || 0;
 
         let cursor = startPoint;
         while (cursor && cursor != endPoint) {
@@ -397,11 +401,24 @@ var Idiomorph = (function () {
             if (softMatch === null) {
               // the current soft match will hard match something else in the future, leave it
               if (!ctx.idMap.has(cursor)) {
-                // save this as the fallback if we get through the loop without finding a hard match
-                softMatch = cursor;
+                // optimization: if node can't id set match, we can just return the soft match immediately
+                if (!nodeMatchCount) {
+                  return cursor;
+                } else {
+                  // save this as the fallback if we get through the loop without finding a hard match
+                  softMatch = cursor;
+                }
               }
             }
           }
+          // check for ids we may be displaced when matching
+          displaceMatchCount += ctx.idMap.get(cursor)?.size || 0;
+          if (displaceMatchCount > nodeMatchCount) {
+            // if we are going to displace more ids than the node contains then
+            // we do not have a good candidate for an id match, so return
+            break;
+          }
+
           if (
             softMatch === null &&
             nextSibling &&

test/ops.js

@@ -188,4 +188,39 @@ describe("morphing operations", function () {
       ],
     );
   });
+
+  it("findBestMatch rejects morphing node that would lose more IDs", function () {
+    // here the findBestMatch function when it finds a node with id's it will track how many
+    // id matches in this node and then as it searches for a matching node it will track
+    // how many id's in the content it would have to remove before it finds a match
+    // if it finds more ids are going to match in-between nodes it aborts matching to
+    // allow better matching with less dom updates.
+    assertOps(
+      `<div>` +
+        `<label>1</label><input id="first">` +
+        `<label>2</label><input id="second">` +
+        `<label>3</label><input id="third">` +
+        `</div>`,
+
+      `<div>` +
+        `<label>3</label><input id="third">` +
+        `<label>1</label><input id="first">` +
+        `<label>2</label><input id="second">` +
+        `</div>`,
+      [
+        [
+          "Morphed",
+          '<div><label>1</label><input id="first"><label>2</label><input id="second"><label>3</label><input id="third"></div>',
+          '<div><label>3</label><input id="third"><label>1</label><input id="first"><label>2</label><input id="second"></div>',
+        ],
+        ["Morphed", "<label>1</label>", "<label>3</label>"],
+        ["Morphed", '<input id="third">', '<input id="third">'],
+        ["Added", "<label>1</label>"],
+        ["Morphed", '<input id="first">', '<input id="first">'],
+        ["Morphed", "<label>2</label>", "<label>2</label>"],
+        ["Morphed", '<input id="second">', '<input id="second">'],
+        ["Removed", "<label>3</label>"],
+      ],
+    );
+  });  
 });

test/preserve-focus.js

@@ -232,13 +232,7 @@ describe("Preserves focus where possible", function () {
       "b",
       false,
     );
-    if (hasMoveBefore()) {
-      assertFocus("focused");
-      // TODO moveBefore loses selection on Chrome 131.0.6778.264
-      // expect will be fixed in future release
-      // assertFocusAndSelection("focused", "b");
-    } else {
-      assertNoFocus();
-    }
+
+    assertFocus("focused");
   });
 });