⚡ Bolt: DocumentFragment를 사용한 DOM 조작 최적화

.jules/bolt.md

@@ -19,3 +19,7 @@
 ## 2026-07-13 - 단일 패스 문자열 치환 최적화 (O(N) 단일 스캔 및 지연 할당)
 **Learning:** `String.replace()`를 여러 번 체이닝하여 호출하면, 문자열 치환이 발생하지 않는 경우에도 내부적으로 불필요한 스캔이 중복 발생하고, 치환 시마다 새로운 문자열 객체와 char 배열이 할당되어 메모리 낭비와 성능 저하(GC 압박)가 발생한다.
 **Action:** 여러 문자를 한 번에 치환해야 하는 경우, O(N) 단일 스캔을 통해 `charAt()`으로 문자를 확인하고, 치환이 실제로 필요한 경우에만 `StringBuilder`를 지연 할당(Lazy allocation)하여 성능을 최적화하고 불필요한 메모리 할당을 방지한다.
+
+## 2024-10-14 - Optimizing DOM mutations with DocumentFragment
+**Learning:** In frontend performance optimization, replacing loop-based `appendChild` calls with a `DocumentFragment` reduces redundant reflows. When optimizing utility functions (like `addDetailRow`), all internal call sites must be tracked down and updated to accept the fragment object to avoid `ReferenceError` crashes. Additionally, custom mock DOM setups in test files must implement a `MockDocumentFragment` that correctly pushes its `childNodes` upon `appendChild` in the parent node mock, instead of appending the fragment itself, simulating standard browser DOM behavior.
+**Action:** When migrating UI renders to use `DocumentFragment`, always use tools like `grep -rn` to verify all utility call sites are updated, and ensure the mock environment fully supports `DocumentFragment` unpacking in `appendChild` before claiming victory.

src/main/resources/static/assets/viewer/demo.js

@@ -114,6 +114,8 @@ function renderHistory(history = loadHistory()) {
   el.historyBody.textContent = "";
   el.emptyHistory.hidden = history.length > 0;
 
+  const fragment = document.createDocumentFragment();
+
   for (const job of history) {
     const row = document.createElement("tr");
     const fileCell = document.createElement("td");
@@ -143,18 +145,19 @@ function renderHistory(history = loadHistory()) {
     }
 
     row.append(fileCell, statusCell, submittedCell, actionsCell);
-    el.historyBody.appendChild(row);
+    fragment.appendChild(row);
   }
 
+  el.historyBody.appendChild(fragment);
   renderRecoveryEvidence(history);
 }
 
-function addDetailRow(label, value) {
+function addDetailRow(fragment, label, value) {
   const term = document.createElement("dt");
   const description = document.createElement("dd");
   term.textContent = label;
   description.textContent = formatDetailValue(value);
-  el.jobDetailBody.append(term, description);
+  fragment.append(term, description);
 }
 
 function formatDetailValue(value) {
@@ -177,17 +180,21 @@ function renderJobDetail(detail) {
     : "Operational evidence";
   el.jobDetailBody.textContent = "";
 
-  addDetailRow("Job ID", detail.jobId);
-  addDetailRow("Tenant", detail.tenantId);
-  addDetailRow("Status", detail.status);
-  addDetailRow("Message", detail.message);
-  addDetailRow("Attempts", `${detail.attemptCount ?? 0} / ${detail.maxAttempts ?? "n/a"}`);
-  addDetailRow("Dead-lettered", Boolean(detail.deadLettered));
-  addDetailRow("Retry at", detail.retryAt);
-  addDetailRow("Created", detail.createdAt);
-  addDetailRow("Started", detail.startedAt);
-  addDetailRow("Completed", detail.completedAt);
-  addDetailRow("Artifact", detail.convertedResourcePath);
+  const fragment = document.createDocumentFragment();
+
+  addDetailRow(fragment, "Job ID", detail.jobId);
+  addDetailRow(fragment, "Tenant", detail.tenantId);
+  addDetailRow(fragment, "Status", detail.status);
+  addDetailRow(fragment, "Message", detail.message);
+  addDetailRow(fragment, "Attempts", `${detail.attemptCount ?? 0} / ${detail.maxAttempts ?? "n/a"}`);
+  addDetailRow(fragment, "Dead-lettered", Boolean(detail.deadLettered));
+  addDetailRow(fragment, "Retry at", detail.retryAt);
+  addDetailRow(fragment, "Created", detail.createdAt);
+  addDetailRow(fragment, "Started", detail.startedAt);
+  addDetailRow(fragment, "Completed", detail.completedAt);
+  addDetailRow(fragment, "Artifact", detail.convertedResourcePath);
+
+  el.jobDetailBody.appendChild(fragment);
 
   el.retryJobBtn.hidden = !detail.deadLettered;
 }

src/test/js/demo-integration.test.mjs

@@ -1,7 +1,7 @@
 import assert from "node:assert/strict";
 import test from "node:test";
 
-import { MockElement } from "./mock-dom.mjs";
+import { MockElement, MockDocumentFragment } from "./mock-dom.mjs";
 
 const elementIds = [
   "upload-form",
@@ -54,6 +54,9 @@ test("the executable demo renders inert actions and blocks repeated status activ
     createElement(tagName) {
       return new MockElement(tagName);
     },
+    createDocumentFragment() {
+      return new MockDocumentFragment();
+    },
   };
   globalThis.window = {
     confirm() {

src/test/js/dom-utils.test.mjs

@@ -6,11 +6,14 @@ import {
   createLink,
   setBusyState
 } from "../../main/resources/static/assets/viewer/dom-utils.js";
-import { MockElement, MockTextNode } from "./mock-dom.mjs";
+import { MockElement, MockTextNode, MockDocumentFragment } from "./mock-dom.mjs";
 
 globalThis.document = {
   createElement(tagName) {
     return new MockElement(tagName);
+  },
+  createDocumentFragment() {
+    return new MockDocumentFragment();
   }
 };
 

src/test/js/mock-dom.mjs

@@ -1,3 +1,30 @@
+export class MockDocumentFragment {
+  constructor() {
+    this.childNodes = [];
+  }
+
+  appendChild(node) {
+    if (node instanceof MockDocumentFragment) {
+      this.childNodes.push(...node.childNodes);
+      node.childNodes = [];
+      return node;
+    }
+    this.childNodes.push(node);
+    return node;
+  }
+
+  append(...nodes) {
+    for (const node of nodes) {
+      if (node instanceof MockDocumentFragment) {
+        this.childNodes.push(...node.childNodes);
+        node.childNodes = [];
+      } else {
+        this.childNodes.push(node);
+      }
+    }
+  }
+}
+
 export class MockTextNode {
   constructor(text) {
     this.type = "text";
@@ -31,12 +58,24 @@ export class MockElement {
   }
 
   appendChild(node) {
+    if (node instanceof MockDocumentFragment) {
+      this.childNodes.push(...node.childNodes);
+      node.childNodes = [];
+      return node;
+    }
     this.childNodes.push(node);
     return node;
   }
 
   append(...nodes) {
-    this.childNodes.push(...nodes);
+    for (const node of nodes) {
+      if (node instanceof MockDocumentFragment) {
+        this.childNodes.push(...node.childNodes);
+        node.childNodes = [];
+      } else {
+        this.childNodes.push(node);
+      }
+    }
   }
 
   replaceChildren(...nodes) {