[tools] Move system-analyzer view files to separate directory

- introduce view specific helper.mjs module
- clean up some imports

Bug: v8:10644
Change-Id: I0497c1a962c90f61f2beca667aca4a3f53a11e59
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2545705Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71269}

tools/system-analyzer/helper.mjs

@@ -2,12 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-const KB = 1024;
-const MB = KB * KB;
-const GB = MB * KB;
-const kMillis2Seconds = 1 / 1000;
+export const KB = 1024;
+export const MB = KB * KB;
+export const GB = MB * KB;
+export const kMillis2Seconds = 1 / 1000;
 
-function formatBytes(bytes) {
+export function formatBytes(bytes) {
   const units = ['B', 'KiB', 'MiB', 'GiB'];
   const divisor = 1024;
   let index = 0;
@@ -18,244 +18,10 @@ function formatBytes(bytes) {
   return bytes.toFixed(2) + units[index];
 }
 
-function formatSeconds(millis) {
+export function formatSeconds(millis) {
   return (millis * kMillis2Seconds).toFixed(2) + 's';
 }
 
-class CSSColor {
-  static _cache = new Map();
-
-  static get(name) {
-    let color = this._cache.get(name);
-    if (color !== undefined) return color;
-    const style = getComputedStyle(document.body);
-    color = style.getPropertyValue(`--${name}`);
-    if (color === undefined) {
-      throw new Error(`CSS color does not exist: ${name}`);
-    }
-    this._cache.set(name, color);
-    return color;
-  }
-  static reset() {
-    this._cache.clear();
-  }
-
-  static get backgroundColor() {
-    return this.get('background-color');
-  }
-  static get surfaceColor() {
-    return this.get('surface-color');
-  }
-  static get primaryColor() {
-    return this.get('primary-color');
-  }
-  static get secondaryColor() {
-    return this.get('secondary-color');
-  }
-  static get onSurfaceColor() {
-    return this.get('on-surface-color');
-  }
-  static get onBackgroundColor() {
-    return this.get('on-background-color');
-  }
-  static get onPrimaryColor() {
-    return this.get('on-primary-color');
-  }
-  static get onSecondaryColor() {
-    return this.get('on-secondary-color');
-  }
-  static get defaultColor() {
-    return this.get('default-color');
-  }
-  static get errorColor() {
-    return this.get('error-color');
-  }
-  static get mapBackgroundColor() {
-    return this.get('map-background-color');
-  }
-  static get timelineBackgroundColor() {
-    return this.get('timeline-background-color');
-  }
-  static get red() {
-    return this.get('red');
-  }
-  static get green() {
-    return this.get('green');
-  }
-  static get yellow() {
-    return this.get('yellow');
-  }
-  static get blue() {
-    return this.get('blue');
-  }
-  static get orange() {
-    return this.get('orange');
-  }
-  static get violet() {
-    return this.get('violet');
-  }
-}
-
-function typeToColor(type) {
-  switch (type) {
-    case 'new':
-      return CSSColor.green;
-    case 'Normalize':
-      return CSSColor.violet;
-    case 'SlowToFast':
-      return CSSColor.orange;
-    case 'InitialMap':
-      return CSSColor.yellow;
-    case 'Transition':
-      return CSSColor.primaryColor;
-    case 'ReplaceDescriptors':
-      return CSSColor.red;
-    case 'LoadGlobalIC':
-      return CSSColor.green;
-    case 'LoadIC':
-      return CSSColor.primaryColor;
-    case 'StoreInArrayLiteralIC':
-      return CSSColor.violet;
-    case 'StoreGlobalIC':
-      return CSSColor.blue;
-    case 'StoreIC':
-      return CSSColor.orange;
-    case 'KeyedLoadIC':
-      return CSSColor.red;
-    case 'KeyedStoreIC':
-      return CSSColor.yellow;
-  }
-  return CSSColor.secondaryColor;
-}
-
-class DOM {
-  static div(classes) {
-    const node = document.createElement('div');
-    if (classes !== void 0) {
-      if (typeof classes === 'string') {
-        node.className = classes;
-      } else {
-        classes.forEach(cls => node.classList.add(cls));
-      }
-    }
-    return node;
-  }
-
-  static table(className) {
-    const node = document.createElement('table');
-    if (className) node.className = className;
-    return node;
-  }
-
-  static td(textOrNode, className) {
-    const node = document.createElement('td');
-    if (typeof textOrNode === 'object') {
-      node.appendChild(textOrNode);
-    } else if (textOrNode) {
-      node.innerText = textOrNode;
-    }
-    if (className) node.className = className;
-    return node;
-  }
-
-  static tr(className) {
-    const node = document.createElement('tr');
-    if (className) node.className = className;
-    return node;
-  }
-
-  static text(string) {
-    return document.createTextNode(string);
-  }
-
-  static removeAllChildren(node) {
-    let range = document.createRange();
-    range.selectNodeContents(node);
-    range.deleteContents();
-  }
-
-  static defineCustomElement(path, generator) {
-    let name = path.substring(path.lastIndexOf('/') + 1, path.length);
-    path = path + '-template.html';
-    fetch(path)
-        .then(stream => stream.text())
-        .then(
-            templateText =>
-                customElements.define(name, generator(templateText)));
-  }
-}
-
-function $(id) {
-  return document.querySelector(id)
-}
-
-class V8CustomElement extends HTMLElement {
-  _updateTimeoutId;
-  _updateCallback = this._update.bind(this);
-
-  constructor(templateText) {
-    super();
-    const shadowRoot = this.attachShadow({mode: 'open'});
-    shadowRoot.innerHTML = templateText;
-    this._updateCallback = this._update.bind(this);
-  }
-
-  $(id) {
-    return this.shadowRoot.querySelector(id);
-  }
-
-  querySelectorAll(query) {
-    return this.shadowRoot.querySelectorAll(query);
-  }
-
-  update() {
-    // Use timeout tasks to asynchronously update the UI without blocking.
-    clearTimeout(this._updateTimeoutId);
-    const kDelayMs = 5;
-    this._updateTimeoutId = setTimeout(this._updateCallback, kDelayMs);
-  }
-
-  _update() {
-    throw Error('Subclass responsibility');
-  }
-}
-
-class LazyTable {
-  constructor(table, rowData, rowElementCreator) {
-    this._table = table;
-    this._rowData = rowData;
-    this._rowElementCreator = rowElementCreator;
-    const tbody = table.querySelector('tbody');
-    table.replaceChild(document.createElement('tbody'), tbody);
-    table.querySelector('tfoot td').onclick = (e) => this._addMoreRows();
-    this._addMoreRows();
-  }
-
-  _nextRowDataSlice() {
-    return this._rowData.splice(0, 100);
-  }
-
-  _addMoreRows() {
-    const fragment = new DocumentFragment();
-    for (let row of this._nextRowDataSlice()) {
-      const tr = this._rowElementCreator(row);
-      fragment.appendChild(tr);
-    }
-    this._table.querySelector('tbody').appendChild(fragment);
-  }
-}
-
-function delay(time) {
+export function delay(time) {
   return new Promise(resolver => setTimeout(resolver, time));
-}
-
-export {
-  DOM,
-  $,
-  V8CustomElement,
-  formatBytes,
-  typeToColor,
-  CSSColor,
-  delay,
-  LazyTable,
-};
+}
\ No newline at end of file

tools/system-analyzer/index.html

@@ -8,12 +8,13 @@ found in the LICENSE file. -->
   <title>Indicium</title>
   <!-- <link rel="icon" type="image/png" href="/images/favicon.png"/> -->
 
-  <link rel="modulepreload" href="./log-file-reader.mjs" >
   <link rel="modulepreload" href="./helper.mjs" >
-  <link rel="preload" href="./log-file-reader-template.html" as="fetch" crossorigin="anonymous">
+  <link rel="modulepreload" href="./view/log-file-reader.mjs" >
+  <link rel="modulepreload" href="./view/helper.mjs" >
+  <link rel="preload" href="./view/log-file-reader-template.html" as="fetch" crossorigin="anonymous">
   <script type="module">
     // Force instatiating the log-reader before anything else.
-    import "./log-file-reader.mjs";
+    import "./view/log-file-reader.mjs";
     // Delay loading of the main App
     (async function() {
       let module = await import('./index.mjs');

tools/system-analyzer/index.mjs

@@ -6,11 +6,10 @@ import {SourcePosition} from '../profile.mjs';
 
 import {State} from './app-model.mjs';
 import {FocusEvent, SelectionEvent, SelectTimeEvent} from './events.mjs';
-import {CSSColor} from './helper.mjs';
-import {$} from './helper.mjs';
 import {IcLogEntry} from './log/ic.mjs';
 import {MapLogEntry} from './log/map.mjs';
 import {Processor} from './processor.mjs';
+import {$, CSSColor} from './view/helper.mjs';
 
 class App {
   _state;
@@ -43,11 +42,11 @@ class App {
 
   async runAsyncInitialize() {
     await Promise.all([
-      import('./ic-panel.mjs'),
-      import('./timeline-panel.mjs'),
-      import('./stats-panel.mjs'),
-      import('./map-panel.mjs'),
-      import('./source-panel.mjs'),
+      import('./view/ic-panel.mjs'),
+      import('./view/timeline-panel.mjs'),
+      import('./view/stats-panel.mjs'),
+      import('./view/map-panel.mjs'),
+      import('./view/source-panel.mjs'),
     ]);
     document.addEventListener(
         'keydown', e => this._navigation?.handleKeyDown(e));

tools/system-analyzer/view/helper.mjs

+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+class CSSColor {
+  static _cache = new Map();
+
+  static get(name) {
+    let color = this._cache.get(name);
+    if (color !== undefined) return color;
+    const style = getComputedStyle(document.body);
+    color = style.getPropertyValue(`--${name}`);
+    if (color === undefined) {
+      throw new Error(`CSS color does not exist: ${name}`);
+    }
+    this._cache.set(name, color);
+    return color;
+  }
+  static reset() {
+    this._cache.clear();
+  }
+
+  static get backgroundColor() {
+    return this.get('background-color');
+  }
+  static get surfaceColor() {
+    return this.get('surface-color');
+  }
+  static get primaryColor() {
+    return this.get('primary-color');
+  }
+  static get secondaryColor() {
+    return this.get('secondary-color');
+  }
+  static get onSurfaceColor() {
+    return this.get('on-surface-color');
+  }
+  static get onBackgroundColor() {
+    return this.get('on-background-color');
+  }
+  static get onPrimaryColor() {
+    return this.get('on-primary-color');
+  }
+  static get onSecondaryColor() {
+    return this.get('on-secondary-color');
+  }
+  static get defaultColor() {
+    return this.get('default-color');
+  }
+  static get errorColor() {
+    return this.get('error-color');
+  }
+  static get mapBackgroundColor() {
+    return this.get('map-background-color');
+  }
+  static get timelineBackgroundColor() {
+    return this.get('timeline-background-color');
+  }
+  static get red() {
+    return this.get('red');
+  }
+  static get green() {
+    return this.get('green');
+  }
+  static get yellow() {
+    return this.get('yellow');
+  }
+  static get blue() {
+    return this.get('blue');
+  }
+  static get orange() {
+    return this.get('orange');
+  }
+  static get violet() {
+    return this.get('violet');
+  }
+}
+
+const kColors = [
+  CSSColor.green,
+  CSSColor.violet,
+  CSSColor.orange,
+  CSSColor.yellow,
+  CSSColor.primaryColor,
+  CSSColor.red,
+  CSSColor.blue,
+  CSSColor.yellow,
+  CSSColor.secondaryColor,
+];
+
+class DOM {
+  static div(classes) {
+    const node = document.createElement('div');
+    if (classes !== void 0) {
+      if (typeof classes === 'string') {
+        node.className = classes;
+      } else {
+        classes.forEach(cls => node.classList.add(cls));
+      }
+    }
+    return node;
+  }
+
+  static table(className) {
+    const node = document.createElement('table');
+    if (className) node.className = className;
+    return node;
+  }
+
+  static td(textOrNode, className) {
+    const node = document.createElement('td');
+    if (typeof textOrNode === 'object') {
+      node.appendChild(textOrNode);
+    } else if (textOrNode) {
+      node.innerText = textOrNode;
+    }
+    if (className) node.className = className;
+    return node;
+  }
+
+  static tr(className) {
+    const node = document.createElement('tr');
+    if (className) node.className = className;
+    return node;
+  }
+
+  static text(string) {
+    return document.createTextNode(string);
+  }
+
+  static removeAllChildren(node) {
+    let range = document.createRange();
+    range.selectNodeContents(node);
+    range.deleteContents();
+  }
+
+  static defineCustomElement(path, generator) {
+    let name = path.substring(path.lastIndexOf('/') + 1, path.length);
+    path = path + '-template.html';
+    fetch(path)
+        .then(stream => stream.text())
+        .then(
+            templateText =>
+                customElements.define(name, generator(templateText)));
+  }
+}
+
+function $(id) {
+  return document.querySelector(id)
+}
+
+class V8CustomElement extends HTMLElement {
+  _updateTimeoutId;
+  _updateCallback = this._update.bind(this);
+
+  constructor(templateText) {
+    super();
+    const shadowRoot = this.attachShadow({mode: 'open'});
+    shadowRoot.innerHTML = templateText;
+    this._updateCallback = this._update.bind(this);
+  }
+
+  $(id) {
+    return this.shadowRoot.querySelector(id);
+  }
+
+  querySelectorAll(query) {
+    return this.shadowRoot.querySelectorAll(query);
+  }
+
+  update() {
+    // Use timeout tasks to asynchronously update the UI without blocking.
+    clearTimeout(this._updateTimeoutId);
+    const kDelayMs = 5;
+    this._updateTimeoutId = setTimeout(this._updateCallback, kDelayMs);
+  }
+
+  _update() {
+    throw Error('Subclass responsibility');
+  }
+}
+
+class LazyTable {
+  constructor(table, rowData, rowElementCreator) {
+    this._table = table;
+    this._rowData = rowData;
+    this._rowElementCreator = rowElementCreator;
+    const tbody = table.querySelector('tbody');
+    table.replaceChild(document.createElement('tbody'), tbody);
+    table.querySelector('tfoot td').onclick = (e) => this._addMoreRows();
+    this._addMoreRows();
+  }
+
+  _nextRowDataSlice() {
+    return this._rowData.splice(0, 100);
+  }
+
+  _addMoreRows() {
+    const fragment = new DocumentFragment();
+    for (let row of this._nextRowDataSlice()) {
+      const tr = this._rowElementCreator(row);
+      fragment.appendChild(tr);
+    }
+    this._table.querySelector('tbody').appendChild(fragment);
+  }
+}
+
+export * from '../helper.mjs';
+export {
+  DOM,
+  $,
+  kColors,
+  V8CustomElement,
+  CSSColor,
+  LazyTable,
+};

tools/system-analyzer/ic-panel.mjs → tools/system-analyzer/view/ic-panel.mjs

@@ -2,14 +2,15 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import {FocusEvent, SelectionEvent, SelectTimeEvent} from './events.mjs';
-import {delay, DOM, V8CustomElement} from './helper.mjs';
-import {Group} from './ic-model.mjs';
-import {IcLogEntry} from './log/ic.mjs';
-import {MapLogEntry} from './log/map.mjs';
+import {FocusEvent, SelectionEvent, SelectTimeEvent} from '../events.mjs';
+import {Group} from '../ic-model.mjs';
+import {IcLogEntry} from '../log/ic.mjs';
+import {MapLogEntry} from '../log/map.mjs';
+
+import {DOM, V8CustomElement} from './helper.mjs';
 
 DOM.defineCustomElement(
-    'ic-panel', (templateText) => class ICPanel extends V8CustomElement {
+    'view/ic-panel', (templateText) => class ICPanel extends V8CustomElement {
       _selectedLogEntries;
       _timeline;
 

tools/system-analyzer/log-file-reader.mjs → tools/system-analyzer/view/log-file-reader.mjs

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 import {DOM, V8CustomElement} from './helper.mjs';
 
-DOM.defineCustomElement('log-file-reader',
+DOM.defineCustomElement('view/log-file-reader',
                         (templateText) =>
                             class LogFileReader extends V8CustomElement {
   constructor() {

tools/system-analyzer/map-panel.mjs → tools/system-analyzer/view/map-panel.mjs

@@ -5,11 +5,12 @@ import './stats-panel.mjs';
 import './map-panel/map-details.mjs';
 import './map-panel/map-transitions.mjs';
 
-import {FocusEvent} from './events.mjs';
+import {FocusEvent} from '../events.mjs';
+import {MapLogEntry} from '../log/map.mjs';
+
 import {DOM, V8CustomElement} from './helper.mjs';
-import {MapLogEntry} from './log/map.mjs';
 
-DOM.defineCustomElement('map-panel',
+DOM.defineCustomElement('view/map-panel',
                         (templateText) =>
                             class MapPanel extends V8CustomElement {
   _map;

tools/system-analyzer/map-panel/map-details.mjs → tools/system-analyzer/view/map-panel/map-details.mjs

 // Copyright 2020 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-import {FocusEvent} from '../events.mjs';
+import {FocusEvent} from '../../events.mjs';
 import {DOM, V8CustomElement} from '../helper.mjs';
 
 DOM.defineCustomElement(
-    './map-panel/map-details',
+    './view/map-panel/map-details',
     (templateText) => class MapDetails extends V8CustomElement {
       _map;
 

tools/system-analyzer/map-panel/map-transitions.mjs → tools/system-analyzer/view/map-panel/map-transitions.mjs

 // Copyright 2020 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-import {FocusEvent, SelectionEvent} from '../events.mjs';
-import {DOM, typeToColor, V8CustomElement} from '../helper.mjs';
+import {FocusEvent, SelectionEvent} from '../../events.mjs';
+import {CSSColor} from '../helper.mjs';
+import {DOM, V8CustomElement} from '../helper.mjs';
 
 DOM.defineCustomElement(
-    './map-panel/map-transitions',
+    './view/map-panel/map-transitions',
     (templateText) => class MapTransitions extends V8CustomElement {
       _map;
       _selectedMapLogEntries;
@@ -38,6 +39,35 @@ DOM.defineCustomElement(
         this._showMap();
       }
 
+      set selectedMapLogEntries(list) {
+        this._selectedMapLogEntries = list;
+        this.update();
+      }
+
+      get selectedMapLogEntries() {
+        return this._selectedMapLogEntries;
+      }
+
+      _typeToColor(type) {
+        switch (type) {
+          case 'new':
+            return CSSColor.green;
+          case 'Normalize':
+            return CSSColor.violet;
+          case 'SlowToFast':
+            return CSSColor.orange;
+          case 'InitialMap':
+            return CSSColor.yellow;
+          case 'Transition':
+            return CSSColor.primaryColor;
+          case 'ReplaceDescriptors':
+            return CSSColor.red;
+          case 'LoadGlobalIC':
+            return CSSColor.green;
+        }
+        return CSSColor.secondaryColor;
+      }
+
       _handleTransitionViewChange(e) {
         this.tooltip.style.left = e.pageX + 'px';
         this.tooltip.style.top = e.pageY + 'px';
@@ -69,15 +99,6 @@ DOM.defineCustomElement(
         this.transitionView.style.display = '';
       }
 
-      set selectedMapLogEntries(list) {
-        this._selectedMapLogEntries = list;
-        this.update();
-      }
-
-      get selectedMapLogEntries() {
-        return this._selectedMapLogEntries;
-      }
-
       _addMapAndParentTransitions(map) {
         if (map === void 0) return;
         if (this._displayedMapsInTree.has(map)) return;
@@ -116,7 +137,7 @@ DOM.defineCustomElement(
       _addTransitionEdge(map) {
         let classes = ['transitionEdge'];
         let edge = DOM.div(classes);
-        edge.style.backgroundColor = typeToColor(map.edge);
+        edge.style.backgroundColor = this._typeToColor(map.edge);
         let labelNode = DOM.div('transitionLabel');
         labelNode.innerText = map.edge.toString();
         edge.appendChild(labelNode);
@@ -145,7 +166,7 @@ DOM.defineCustomElement(
 
       _addMapNode(map) {
         let node = DOM.div('map');
-        if (map.edge) node.style.backgroundColor = typeToColor(map.edge);
+        if (map.edge) node.style.backgroundColor = this._typeToColor(map.edge);
         node.map = map;
         node.onclick = this._selectMapHandler
         if (map.children.length > 1) {

tools/system-analyzer/source-panel.mjs → tools/system-analyzer/view/source-panel.mjs

 // Copyright 2020 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-import {FocusEvent, SelectionEvent} from './events.mjs';
+import {FocusEvent, SelectionEvent} from '../events.mjs';
+import {IcLogEntry} from '../log/ic.mjs';
+import {MapLogEntry} from '../log/map.mjs';
+
 import {delay, DOM, formatBytes, V8CustomElement} from './helper.mjs';
-import {IcLogEntry} from './log/ic.mjs';
-import {MapLogEntry} from './log/map.mjs';
 
-DOM.defineCustomElement('source-panel',
+DOM.defineCustomElement('view/source-panel',
                         (templateText) =>
                             class SourcePanel extends V8CustomElement {
   _selectedSourcePositions = [];

tools/system-analyzer/stats-panel.mjs → tools/system-analyzer/view/stats-panel.mjs

 // Copyright 2020 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-import {SelectionEvent} from './events.mjs';
-import {DOM, V8CustomElement} from './helper.mjs';
-import {delay, LazyTable} from './helper.mjs';
+import {SelectionEvent} from '../events.mjs';
+
+import {DOM, LazyTable, V8CustomElement} from './helper.mjs';
 
 DOM.defineCustomElement(
-    'stats-panel', (templateText) => class StatsPanel extends V8CustomElement {
+    'view/stats-panel',
+    (templateText) => class StatsPanel extends V8CustomElement {
       _timeline;
       _transitions;
       _selectedLogEntries;

tools/system-analyzer/timeline-panel.mjs → tools/system-analyzer/view/timeline-panel.mjs

@@ -4,11 +4,11 @@
 
 import './timeline/timeline-track.mjs';
 
-import {SynchronizeSelectionEvent} from './events.mjs';
+import {SynchronizeSelectionEvent} from '../events.mjs';
 import {DOM, V8CustomElement} from './helper.mjs';
 
 DOM.defineCustomElement(
-    'timeline-panel',
+    'view/timeline-panel',
     (templateText) => class TimelinePanel extends V8CustomElement {
       constructor() {
         super(templateText);

tools/system-analyzer/timeline/timeline-track.mjs → tools/system-analyzer/view/timeline/timeline-track.mjs

@@ -2,10 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import {FocusEvent, SelectionEvent, SelectTimeEvent, SynchronizeSelectionEvent} from '../events.mjs';
-import {CSSColor, delay, DOM, V8CustomElement} from '../helper.mjs';
-import {kChunkHeight, kChunkWidth} from '../log/map.mjs';
-import {MapLogEntry} from '../log/map.mjs';
+import {FocusEvent, SelectionEvent, SelectTimeEvent, SynchronizeSelectionEvent} from '../../events.mjs';
+import {kChunkHeight, kChunkWidth} from '../../log/map.mjs';
+import {MapLogEntry} from '../../log/map.mjs';
+import {CSSColor, DOM, V8CustomElement} from '../helper.mjs';
 
 const kColors = [
   CSSColor.green,
@@ -19,7 +19,7 @@ const kColors = [
   CSSColor.secondaryColor,
 ];
 
-DOM.defineCustomElement('./timeline/timeline-track',
+DOM.defineCustomElement('view/timeline/timeline-track',
                         (templateText) =>
                             class TimelineTrack extends V8CustomElement {
   // TODO turn into static field once Safari supports it.