perf(table): Slightly improve speed of adding/remvoing sticky styles

src/cdk/table/sticky-styler.ts

@@ -21,6 +21,7 @@ export type StickyDirection = 'top' | 'bottom' | 'left' | 'right';
  */
 export const STICKY_DIRECTIONS: StickyDirection[] = ['top', 'bottom', 'left', 'right'];
 
+
 /**
  * Applies and removes sticky positioning styles to the `CdkTable` rows and columns cells.
  * @docs-private
@@ -34,12 +35,16 @@ export class StickyStyler {
    * @param direction The directionality context of the table (ltr/rtl); affects column positioning
    *     by reversing left/right positions.
    * @param _isBrowser Whether the table is currently being rendered on the server or the client.
+   * @param _needsPositionStickyOnElement Whether we need to specify position: sticky on cells
+   *     using inline styles. If false, it is assumed that position: sticky is included in
+   *     the component stylesheet for _stickCellCss.
    */
   constructor(private _isNativeHtmlTable: boolean,
               private _stickCellCss: string,
               public direction: Direction,
               private _coalescedStyleScheduler: _CoalescedStyleScheduler,
-              private _isBrowser = true) { }
+              private _isBrowser = true,
+              private readonly _needsPositionStickyOnElement = true) { }
 
   /**
    * Clears the sticky positioning styles from the row and its cells by resetting the `position`
@@ -204,13 +209,21 @@ export class StickyStyler {
     for (const dir of stickyDirections) {
       element.style[dir] = '';
     }
-    element.style.zIndex = this._getCalculatedZIndex(element);
 
     // If the element no longer has any more sticky directions, remove sticky positioning and
     // the sticky CSS class.
-    const hasDirection = STICKY_DIRECTIONS.some(dir => !!element.style[dir]);
-    if (!hasDirection) {
-      element.style.position = '';
+    // Short-circuit checking element.style[dir] for stickyDirections as they
+    // were already removed above.
+    const hasDirection = STICKY_DIRECTIONS.some(dir =>
+        stickyDirections.indexOf(dir) === -1 && element.style[dir]);
+    if (hasDirection) {
+      element.style.zIndex = this._getCalculatedZIndex(element);
+    } else {
+      // When not hasDirection, _getCalculatedZIndex will always return ''.
+      element.style.zIndex = '';
+      if (this._needsPositionStickyOnElement) {
+        element.style.position = '';
+      }
       element.classList.remove(this._stickCellCss);
     }
   }
@@ -223,8 +236,10 @@ export class StickyStyler {
   _addStickyStyle(element: HTMLElement, dir: StickyDirection, dirValue: number) {
     element.classList.add(this._stickCellCss);
     element.style[dir] = `${dirValue}px`;
-    element.style.cssText += 'position: -webkit-sticky; position: sticky; ';
     element.style.zIndex = this._getCalculatedZIndex(element);
+    if (this._needsPositionStickyOnElement) {
+      element.style.cssText += 'position: -webkit-sticky; position: sticky; ';
+    }
   }
 
   /**

src/cdk/table/table.ts

@@ -321,6 +321,13 @@ export class CdkTable<T> implements AfterContentChecked, CollectionViewer, OnDes
    */
   protected stickyCssClass: string = 'cdk-table-sticky';
 
+  /**
+   * Whether to manually add positon: sticky to all sticky cell elements. Not needed if
+   * the position is set in a selector associated with the value of stickyCssClass. May be
+   * overridden by table subclasses
+   */
+  protected needsPositionStickyOnElement = true;
+
   /** Whether the no data row is currently showing anything. */
   private _isShowingNoDataRow = false;
 
@@ -1119,7 +1126,7 @@ export class CdkTable<T> implements AfterContentChecked, CollectionViewer, OnDes
     const direction: Direction = this._dir ? this._dir.value : 'ltr';
     this._stickyStyler = new StickyStyler(
         this._isNativeHtmlTable, this.stickyCssClass, direction, this._coalescedStyleScheduler,
-        this._platform.isBrowser);
+        this._platform.isBrowser, this.needsPositionStickyOnElement);
     (this._dir ? this._dir.change : observableOf<Direction>())
     .pipe(takeUntil(this._onDestroy))
     .subscribe(value => {

src/material-experimental/mdc-table/BUILD.bazel

@@ -44,6 +44,7 @@ sass_binary(
     deps = [
         "//src/material-experimental/mdc-helpers:mdc_helpers_scss_lib",
         "//src/material-experimental/mdc-helpers:mdc_scss_deps_lib",
+        "//src/material/core:core_scss_lib",
     ],
 )
 

src/material-experimental/mdc-table/table.scss

@@ -1,4 +1,9 @@
+@use '../../material/core/style/vendor-prefixes';
 @import '@material/data-table/mixins.import';
 @import '../mdc-helpers/mdc-helpers';
 
 @include mdc-data-table-core-styles($query: $mat-base-styles-without-animation-query);
+
+.mat-table-sticky {
+  @include vendor-prefixes.position-sticky;
+}

src/material-experimental/mdc-table/table.ts

@@ -34,6 +34,9 @@ export class MatTable<T> extends CdkTable<T> implements OnInit {
   /** Overrides the sticky CSS class set by the `CdkTable`. */
   protected stickyCssClass = 'mat-mdc-table-sticky';
 
+  /** Overrides the need to add position: sticky on every sticky cell element in `CdkTable`. */
+  protected needsPositionStickyOnElement = false;
+
   // After ngOnInit, the `CdkTable` has created and inserted the table sections (thead, tbody,
   // tfoot). MDC requires the `mdc-data-table__content` class to be added to the body.
   ngOnInit() {

src/material/core/style/_vendor-prefixes.scss

@@ -38,4 +38,9 @@
   -webkit-backface-visibility: $value;
   backface-visibility: $value;
 }
+
+@mixin position-sticky {
+  position: -webkit-sticky;
+  position: sticky;
+}
 /* stylelint-enable */

src/material/table/BUILD.bazel

@@ -38,6 +38,7 @@ sass_library(
 sass_binary(
     name = "table_scss",
     src = "table.scss",
+    deps = ["//src/material/core:core_scss_lib"],
 )
 
 ng_test_library(

src/material/table/table.scss

@@ -1,3 +1,5 @@
+@use '../core/style/vendor-prefixes';
+
 $mat-header-row-height: 56px;
 $mat-row-height: 48px;
 $mat-row-horizontal-padding: 24px;
@@ -114,3 +116,7 @@ th.mat-header-cell:last-of-type, td.mat-cell:last-of-type, td.mat-footer-cell:la
     padding-left: $mat-row-horizontal-padding;
   }
 }
+
+.mat-table-sticky {
+  @include vendor-prefixes.position-sticky;
+}

src/material/table/table.ts

@@ -42,4 +42,7 @@ import {_DisposeViewRepeaterStrategy, _VIEW_REPEATER_STRATEGY} from '@angular/cd
 export class MatTable<T> extends CdkTable<T> {
   /** Overrides the sticky CSS class set by the `CdkTable`. */
   protected stickyCssClass = 'mat-table-sticky';
+
+  /** Overrides the need to add position: sticky on every sticky cell element in `CdkTable`. */
+  protected needsPositionStickyOnElement = false;
 }

tools/public_api_guard/cdk/table.d.ts

@@ -203,6 +203,7 @@ export declare class CdkTable<T> implements AfterContentChecked, CollectionViewe
     set dataSource(dataSource: CdkTableDataSourceInput<T>);
     get multiTemplateDataRows(): boolean;
     set multiTemplateDataRows(v: boolean);
+    protected needsPositionStickyOnElement: boolean;
     protected stickyCssClass: string;
     get trackBy(): TrackByFunction<T>;
     set trackBy(fn: TrackByFunction<T>);
@@ -315,7 +316,7 @@ export declare type StickyDirection = 'top' | 'bottom' | 'left' | 'right';
 
 export declare class StickyStyler {
     direction: Direction;
-    constructor(_isNativeHtmlTable: boolean, _stickCellCss: string, direction: Direction, _coalescedStyleScheduler: _CoalescedStyleScheduler, _isBrowser?: boolean);
+    constructor(_isNativeHtmlTable: boolean, _stickCellCss: string, direction: Direction, _coalescedStyleScheduler: _CoalescedStyleScheduler, _isBrowser?: boolean, _needsPositionStickyOnElement?: boolean);
     _addStickyStyle(element: HTMLElement, dir: StickyDirection, dirValue: number): void;
     _getCalculatedZIndex(element: HTMLElement): string;
     _getCellWidths(row: HTMLElement): number[];

tools/public_api_guard/material/table.d.ts

@@ -76,6 +76,7 @@ export declare class MatRowDef<T> extends CdkRowDef<T> {
 }
 
 export declare class MatTable<T> extends CdkTable<T> {
+    protected needsPositionStickyOnElement: boolean;
     protected stickyCssClass: string;
     static ɵcmp: i0.ɵɵComponentDefWithMeta<MatTable<any>, "mat-table, table[mat-table]", ["matTable"], {}, {}, never, ["caption", "colgroup, col"]>;
     static ɵfac: i0.ɵɵFactoryDef<MatTable<any>, never>;