refactor(*): removing redundant implementation

Author: ChronosSF

projects/igniteui-angular/migrations/common/util.ts

@@ -188,7 +188,7 @@ export const parseFile = (parser: HtmlParser, host: Tree, filePath: string, enco
 
 export const findElementNodes = (root: Node[], tag: string | string[]): Node[] => {
     const tags = new Set(Array.isArray(tag) ? tag : [tag]);
-    return flatten(Array.isArray(root) ? root : [root])
+    return (Array.isArray(root) ? root : [root]).flat()
         .filter((node: Element) => tags.has(node.name));
 };
 
@@ -232,7 +232,7 @@ export const flatten = (list: Node[]) => {
         r.push(node);
 
         if (isElement(node)) {
-            r = r.concat(flatten((node as Element).children));
+            r = r.concat((node as Element).children.flat());
         }
     }
     return r;

projects/igniteui-angular/src/lib/core/utils.ts

@@ -375,22 +375,6 @@ export class PlatformUtil {
     }
 }
 
-/**
- * @hidden
- */
-export const flatten = (arr: any[]) => {
-    let result = [];
-
-    arr.forEach(el => {
-        result.push(el);
-        if (el.children) {
-            const children = Array.isArray(el.children) ? el.children : el.children.toArray();
-            result = result.concat(flatten(children));
-        }
-    });
-    return result;
-};
-
 export interface CancelableEventArgs {
     /**
      * Provides the ability to cancel the event.

projects/igniteui-angular/src/lib/grids/columns/column-group.component.ts

@@ -12,7 +12,6 @@ import {
 import { takeUntil } from 'rxjs/operators';
 
 import { IgxColumnComponent } from './column.component';
-import { flatten } from '../../core/utils';
 import { CellType, ColumnType, IgxColumnTemplateContext } from '../common/grid.interface';
 
 /* blazorElement */
@@ -351,7 +350,7 @@ export class IgxColumnGroupComponent extends IgxColumnComponent implements After
 
     /** @hidden @internal **/
     public override get allChildren(): IgxColumnComponent[] {
-        return flatten(this.children.toArray());
+        return this.children.toArray().flat();
     }
     /**
      * Returns a boolean indicating if the column is a `ColumnGroup`.

projects/igniteui-angular/src/lib/grids/headers/grid-header-row.component.ts

@@ -11,7 +11,7 @@ import {
     ViewChildren,
     booleanAttribute
 } from '@angular/core';
-import { flatten, trackByIdentity } from '../../core/utils';
+import { trackByIdentity } from '../../core/utils';
 import { IgxGridForOfDirective } from '../../directives/for-of/for_of.directive';
 import { ColumnType, GridType, IgxHeadSelectorTemplateContext } from '../common/grid.interface';
 import { IgxGridFilteringCellComponent } from '../filtering/base/grid-filtering-cell.component';
@@ -80,7 +80,7 @@ export class IgxGridHeaderRowComponent implements DoCheck {
      * @hidden @internal
      */
     public get groups(): IgxGridHeaderGroupComponent[] {
-        return flatten(this._groups?.toArray() ?? []);
+        return (this._groups?.toArray() ?? []).flat();
     }
 
     /** Header components in the header row. */

projects/igniteui-angular/src/lib/grids/hierarchical-grid/hierarchical-grid.component.ts

@@ -66,7 +66,6 @@ import { IgxGridDragSelectDirective } from '../selection/drag-select.directive';
 import { IgxGridBodyDirective } from '../grid.common';
 import { IgxGridHeaderRowComponent } from '../headers/grid-header-row.component';
 import { IgxActionStripToken } from '../../action-strip/token';
-import { flatten } from '../../core/utils';
 import { IFilteringExpressionsTree } from '../../data-operations/filtering-expressions-tree';
 
 let NEXT_ID = 0;
@@ -1269,7 +1268,7 @@ export class IgxHierarchicalGridComponent extends IgxHierarchicalGridBaseDirecti
         let fields = [];
         let childEntities;
         if (!rowIsland.autoGenerate) {
-            fields = flatten(rowIsland.childColumns.toArray()).filter(col => col.field)
+            fields = rowIsland.childColumns.toArray().flat().filter(col => col.field)
                 .map(f => ({ field: f.field, dataType: f.dataType })) as FieldType[];
         } else if (firstRowData) {
             const rowIslandFields = Object.keys(firstRowData).map(key => {