Angular: update Angular Change Detection Specifics section

concepts/40 Angular Components/20 Component Configuration Syntax/85 Angular Change Detection Specifics.md

@@ -2,65 +2,189 @@ Angular activates change detection on each property change. This approach backfi
 
     <!-- tab: app.component.ts -->
     import { Component } from '@angular/core';
+
+    enum GridColumnsOption {
+        PersonalDetails = 0,
+        JobDetails = 1,
+    }
 
     @Component({
-        selector: 'app-root',
+        selector: 'app-component',
         template: `
             <dx-data-grid
-                [columns]="getColumns()">
+                [columns]="getColumns(columnsOption)">
             </dx-data-grid>
         `,
-        styleUrls: ['./app.component.css']
     })
+
     export class AppComponent {
-        getColumns() {
-            return [
-                { dataField: "firstName" },
-                { dataField: "lastName" }
-            ];
+        columnsOption = GridColumnsOption.PersonalDetails;
+
+        getColumns(option: GridColumnsOption): string[] {
+            switch (option) {
+                case GridColumnsOption.PersonalDetails:
+                    return [
+                        'name',
+                        'address',
+                        'phone',
+                    ];
+                case GridColumnsOption.JobDetails:
+                    return [
+                        'name',
+                        'position',
+                        'salary',
+                    ];
+                default:
+                    return [];
+            }
         }
     }
 
 In the code above, the `getColumns()` function returns an array of objects, but this array is created from scratch each time the function is called. This is what happens when you run this code:
 
 1. The `getColumns()` function returns an array.
-1. The array gets assigned to the `columns` property. This activates change detection.
-1. When comparing the old and new `columns` values, the change detection mechanism calls `getColumns()` again and receives a different array.
-1. The array gets assigned to the `columns` property, and the cycle repeats infinitely.
+2. The array gets assigned to the `columns` property. This activates change detection.
+3. When comparing the old and new `columns` values, the change detection mechanism calls `getColumns()` again and receives a different array.
+4. The array gets assigned to the `columns` property, and the cycle repeats infinitely.
+
+To workaround this behavior, implement one of the following approaches:
+
+**Use a component’s class field instead of a method.**
+
+    <!-- tab: app.component.ts -->
+    import { Component } from '@angular/core';
+
+    enum GridColumnsOption {
+        PersonalDetails = 0,
+        JobDetails = 1,
+    }
+
+    @Component({
+        selector: 'app-component',
+        template: `
+            <dx-data-grid
+                [columns]="columns[columnsOption]">
+            </dx-data-grid>
+        `,
+    })
+
+    export class AppComponent {
+        columnsOption = GridColumnsOption.PersonalDetails;
+
+        columns = {
+            [GridColumnsOption.PersonalDetails]: [
+                'name',
+                'address',
+                'phone',
+            ],
+            [GridColumnsOption.JobDetails]: [
+                'name',
+                'position',
+                'salary',
+            ],
+        };
+    }
+
+**Rewrite a component’s class method to the custom [Angular pipe](https://angular.io/guide/pipes-custom-data-trans).**
+
+    <!-- tab: app.component.ts -->
+    import { 
+        Component,
+        Pipe,
+        PipeTransform,
+    } from '@angular/core';
+
+    enum GridColumnsOption {
+        PersonalDetails = 0,
+        JobDetails = 1,
+    }
+
+    @Pipe({name: 'columnsPipe'})
+
+    export class ExponentialStrengthPipe implements PipeTransform {
+        transform(columnsOption: GridColumnsOption): string[] {
+            switch (option) {
+                case GridColumnsOption.PersonalDetails:
+                    return [
+                        'name',
+                        'address',
+                        'phone',
+                    ];
+                case GridColumnsOption.JobDetails:
+                    return [
+                        'name',
+                        'position',
+                        'salary',
+                    ];
+                default:
+                    return [];
+            }
+        }
+    }
+
+    @Component({
+        selector: 'app-component',
+        template: `
+            <dx-data-grid
+                [columns]="columnsOption | columnsPipe">
+            </dx-data-grid>
+        `,
+    })
 
-To workaround this behavior, do one of the following:
+    export class AppComponent {
+        columnsOption = GridColumnsOption.PersonalDetails;
+    } 
 
-- Return an object reference, not a new object, from the function:
+**Cache a returned value of the component’s method (for example, you can use universal apply pipe).** 
 
         <!-- tab: app.component.ts -->
-        import { Component } from '@angular/core';
+        import { 
+            Component,
+            Pipe,
+            PipeTransform, 
+        } from '@angular/core';
+
+        enum GridColumnsOption {
+            PersonalDetails = 0,
+            JobDetails = 1,
+        }
+
+        @Pipe({ name: 'apply' })
+
+        export class ApplyPipe<TArgs, TReturn> implements PipeTransform {
+            transform(func: ((...args: TArgs[]) => TReturn), ...args: TArgs[]): TReturn { return func(...args); }
+        }
 
         @Component({
-            selector: 'app-root',
+            selector: 'app-component',
             template: `
                 <dx-data-grid
-                    [columns]="getColumns()">
+                    [columns]="getColumns | apply: columnsOption">
                 </dx-data-grid>
             `,
-            styleUrls: ['./app.component.css']
         })
+
         export class AppComponent {
-            _columns: [
-                { dataField: "firstName" },
-                { dataField: "lastName" }
-            ];
-            getColumns() {
-                return this._columns;
+            columnsOption = GridColumnsOption.PersonalDetails;
+
+            getColumns = (option: GridColumnsOption): string[] => {
+                switch (option) {
+                    case GridColumnsOption.PersonalDetails:
+                        return [
+                            'name',
+                            'address',
+                            'phone',
+                        ];
+                    case GridColumnsOption.JobDetails:
+                        return [
+                            'firstName',
+                            'position',
+                            'salary',
+                        ];
+                    default:
+                        return [];
+                }
             }
         }
 
-- Switch change detection to the `OnPush` mode:
-
-        <!-- tab: app.component.ts -->
-        import { Component, ChangeDetectionStrategy } from '@angular/core';
-
-        @Component({
-            // ...
-            changeDetection: ChangeDetectionStrategy.OnPush
-        })
-        // ...
+[note]We recommend you to use an arrow function with this approach.