feat(material/chips): prevent chips from being deleted when user holds backspace

src/components-examples/material/chips/chips-autocomplete/chips-autocomplete-example.ts

@@ -34,18 +34,15 @@ export class ChipsAutocompleteExample {
   }
 
   add(event: MatChipInputEvent): void {
-    const input = event.input;
-    const value = event.value;
+    const value = (event.value || '').trim();
 
     // Add our fruit
-    if ((value || '').trim()) {
-      this.fruits.push(value.trim());
+    if (value) {
+      this.fruits.push(value);
     }
 
-    // Reset the input value
-    if (input) {
-      input.value = '';
-    }
+    // Clear the input value
+    event.clearInput();
 
     this.fruitCtrl.setValue(null);
   }

src/components-examples/material/chips/chips-input/chips-input-example.ts

@@ -27,18 +27,15 @@ export class ChipsInputExample {
   ];
 
   add(event: MatChipInputEvent): void {
-    const input = event.input;
-    const value = event.value;
+    const value = (event.value || '').trim();
 
     // Add our fruit
-    if ((value || '').trim()) {
-      this.fruits.push({name: value.trim()});
+    if (value) {
+      this.fruits.push({name: value});
     }
 
-    // Reset the input value
-    if (input) {
-      input.value = '';
-    }
+    // Clear the input value
+    event.clearInput();
   }
 
   remove(fruit: Fruit): void {

src/dev-app/chips/chips-demo.ts

@@ -11,7 +11,6 @@ import {Component} from '@angular/core';
 import {MatChipInputEvent} from '@angular/material/chips';
 import {ThemePalette} from '@angular/material/core';
 
-
 export interface Person {
   name: string;
 }
@@ -61,17 +60,15 @@ export class ChipsDemo {
   }
 
   add(event: MatChipInputEvent): void {
-    const {input, value} = event;
+    const value = (event.value || '').trim();
 
     // Add our person
-    if ((value || '').trim()) {
-      this.people.push({ name: value.trim() });
+    if (value) {
+      this.people.push({ name: value });
     }
 
-    // Reset the input value
-    if (input) {
-      input.value = '';
-    }
+    // Clear the input value
+    event.clearInput();
   }
 
   remove(person: Person): void {

src/material/chips/chip-input.ts

@@ -7,20 +7,32 @@
  */
 
 import {BooleanInput, coerceBooleanProperty} from '@angular/cdk/coercion';
-import {hasModifierKey, TAB} from '@angular/cdk/keycodes';
-import {Directive, ElementRef, EventEmitter, Inject, Input, OnChanges, Output} from '@angular/core';
+import {BACKSPACE, hasModifierKey, TAB} from '@angular/cdk/keycodes';
+import {
+  AfterContentInit, 
+  Directive,
+  ElementRef,
+  EventEmitter,
+  Inject,
+  Input,
+  OnChanges,
+  OnDestroy,
+  Output
+} from '@angular/core';
 import {MatChipsDefaultOptions, MAT_CHIPS_DEFAULT_OPTIONS} from './chip-default-options';
 import {MatChipList} from './chip-list';
 import {MatChipTextControl} from './chip-text-control';
 
-
 /** Represents an input event on a `matChipInput`. */
 export interface MatChipInputEvent {
   /** The native `<input>` element that the event is being fired for. */
   input: HTMLInputElement;
 
   /** The value of the input. */
   value: string;
+
+  /** Call to clear the value of the input */
+  clearInput(): void;
 }
 
 // Increasing integer for generating unique ids.
@@ -36,6 +48,7 @@ let nextUniqueId = 0;
   host: {
     'class': 'mat-chip-input mat-input-element',
     '(keydown)': '_keydown($event)',
+    '(keyup)': '_keyup($event)',
     '(blur)': '_blur()',
     '(focus)': '_focus()',
     '(input)': '_onInput()',
@@ -46,7 +59,10 @@ let nextUniqueId = 0;
     '[attr.aria-required]': '_chipList && _chipList.required || null',
   }
 })
-export class MatChipInput implements MatChipTextControl, OnChanges {
+export class MatChipInput implements MatChipTextControl, OnChanges, OnDestroy, AfterContentInit {
+  /** Used to prevent focus moving to chips while user is holding backspace */
+  private _focusLastChipOnBackspace: boolean;
+
   /** Whether the control is focused. */
   focused: boolean = false;
   _chipList: MatChipList;
@@ -105,21 +121,50 @@ export class MatChipInput implements MatChipTextControl, OnChanges {
     this._inputElement = this._elementRef.nativeElement as HTMLInputElement;
   }
 
-  ngOnChanges() {
+  ngOnChanges(): void {
     this._chipList.stateChanges.next();
   }
 
+  ngOnDestroy(): void {
+    this.chipEnd.complete();
+  }
+
+  ngAfterContentInit(): void {
+    this._focusLastChipOnBackspace = this.empty;
+  }
+
   /** Utility method to make host definition/tests more clear. */
   _keydown(event?: KeyboardEvent) {
-    // Allow the user's focus to escape when they're tabbing forward. Note that we don't
-    // want to do this when going backwards, because focus should go back to the first chip.
-    if (event && event.keyCode === TAB && !hasModifierKey(event, 'shiftKey')) {
-      this._chipList._allowFocusEscape();
+    if (event) {
+      // Allow the user's focus to escape when they're tabbing forward. Note that we don't
+      // want to do this when going backwards, because focus should go back to the first chip.
+      if (event.keyCode === TAB && !hasModifierKey(event, 'shiftKey')) {
+        this._chipList._allowFocusEscape();
+      }
+
+      if (event.keyCode === BACKSPACE && this._focusLastChipOnBackspace) {
+        this._chipList._keyManager.setLastItemActive();
+        event.preventDefault();
+        return;
+      } else {
+        this._focusLastChipOnBackspace = false;
+      }
     }
 
     this._emitChipEnd(event);
   }
 
+  /**
+   * Pass events to the keyboard manager. Available here for tests.
+   */
+  _keyup(event: KeyboardEvent) {
+    // Allow user to move focus to chips next time he presses backspace
+    if (!this._focusLastChipOnBackspace && event.keyCode === BACKSPACE && this.empty) {
+      this._focusLastChipOnBackspace = true;
+      event.preventDefault();
+    }
+  }
+
   /** Checks to see if the blur should emit the (chipEnd) event. */
   _blur() {
     if (this.addOnBlur) {
@@ -143,12 +188,18 @@ export class MatChipInput implements MatChipTextControl, OnChanges {
     if (!this._inputElement.value && !!event) {
       this._chipList._keydown(event);
     }
-    if (!event || this._isSeparatorKey(event)) {
-      this.chipEnd.emit({ input: this._inputElement, value: this._inputElement.value });
 
-      if (event) {
-        event.preventDefault();
-      }
+    if (!event || this._isSeparatorKey(event)) {
+      this.chipEnd.emit({
+        input: this._inputElement,
+        value: this._inputElement.value,
+        clearInput: () => {
+          this._inputElement.value = '';
+          this._focusLastChipOnBackspace = true;
+        }
+      });
+
+      event?.preventDefault();
     }
   }
 

src/material/chips/chip-list.spec.ts

@@ -1516,21 +1516,18 @@ class InputChipList {
   isRequired: boolean;
 
   add(event: MatChipInputEvent): void {
-    let input = event.input;
-    let value = event.value;
+    const value = (event.value || '').trim();
 
     // Add our foods
-    if ((value || '').trim()) {
+    if (value) {
       this.foods.push({
-        value: `${value.trim().toLowerCase()}-${this.foods.length}`,
-        viewValue: value.trim()
+        value: `${value.toLowerCase()}-${this.foods.length}`,
+        viewValue: value
       });
     }
 
-    // Reset the input value
-    if (input) {
-      input.value = '';
-    }
+    // Clear the input value
+    event.clearInput();
   }
 
   remove(food: any): void {

src/material/chips/chip-list.ts

@@ -10,7 +10,6 @@ import {FocusKeyManager} from '@angular/cdk/a11y';
 import {Directionality} from '@angular/cdk/bidi';
 import {BooleanInput, coerceBooleanProperty} from '@angular/cdk/coercion';
 import {SelectionModel} from '@angular/cdk/collections';
-import {BACKSPACE} from '@angular/cdk/keycodes';
 import {
   AfterContentInit,
   ChangeDetectionStrategy,
@@ -42,7 +41,6 @@ import {startWith, takeUntil} from 'rxjs/operators';
 import {MatChip, MatChipEvent, MatChipSelectionChange} from './chip';
 import {MatChipTextControl} from './chip-text-control';
 
-
 // Boilerplate for applying mixins to MatChipList.
 /** @docs-private */
 class MatChipListBase {
@@ -68,7 +66,6 @@ export class MatChipListChange {
     public value: any) { }
 }
 
-
 /**
  * A material design chips component (named ChipList for its similarity to the List component).
  */
@@ -415,7 +412,6 @@ export class MatChipList extends _MatChipListMixinBase implements MatFormFieldCo
     this._dropSubscriptions();
   }
 
-
   /** Associates an HTML input element with this chip list. */
   registerInput(inputElement: MatChipTextControl): void {
     this._chipInput = inputElement;
@@ -499,17 +495,12 @@ export class MatChipList extends _MatChipListMixinBase implements MatFormFieldCo
   _keydown(event: KeyboardEvent) {
     const target = event.target as HTMLElement;
 
-    // If they are on an empty input and hit backspace, focus the last chip
-    if (event.keyCode === BACKSPACE && this._isInputEmpty(target)) {
-      this._keyManager.setLastItemActive();
-      event.preventDefault();
-    } else if (target && target.classList.contains('mat-chip')) {
+    if (target && target.classList.contains('mat-chip')) {
       this._keyManager.onKeydown(event);
       this.stateChanges.next();
     }
   }
 
-
   /**
    * Check the tab index as you should not be allowed to focus an empty list.
    */
@@ -546,15 +537,6 @@ export class MatChipList extends _MatChipListMixinBase implements MatFormFieldCo
     return index >= 0 && index < this.chips.length;
   }
 
-  private _isInputEmpty(element: HTMLElement): boolean {
-    if (element && element.nodeName.toLowerCase() === 'input') {
-      let input = element as HTMLInputElement;
-      return !input.value;
-    }
-
-    return false;
-  }
-
   _setSelectionByValue(value: any, isUserInput: boolean = true) {
     this._clearSelection();
     this.chips.forEach(chip => chip.deselect());

tools/public_api_guard/material/chips.d.ts

@@ -70,7 +70,7 @@ export interface MatChipEvent {
     chip: MatChip;
 }
 
-export declare class MatChipInput implements MatChipTextControl, OnChanges {
+export declare class MatChipInput implements MatChipTextControl, OnChanges, OnDestroy, AfterContentInit {
     _addOnBlur: boolean;
     _chipList: MatChipList;
     protected _elementRef: ElementRef<HTMLInputElement>;
@@ -91,9 +91,12 @@ export declare class MatChipInput implements MatChipTextControl, OnChanges {
     _emitChipEnd(event?: KeyboardEvent): void;
     _focus(): void;
     _keydown(event?: KeyboardEvent): void;
+    _keyup(event: KeyboardEvent): void;
     _onInput(): void;
     focus(options?: FocusOptions): void;
+    ngAfterContentInit(): void;
     ngOnChanges(): void;
+    ngOnDestroy(): void;
     static ngAcceptInputType_addOnBlur: BooleanInput;
     static ngAcceptInputType_disabled: BooleanInput;
     static ɵdir: i0.ɵɵDirectiveDefWithMeta<MatChipInput, "input[matChipInputFor]", ["matChipInput", "matChipInputFor"], { "chipList": "matChipInputFor"; "addOnBlur": "matChipInputAddOnBlur"; "separatorKeyCodes": "matChipInputSeparatorKeyCodes"; "placeholder": "placeholder"; "id": "id"; "disabled": "disabled"; }, { "chipEnd": "matChipInputTokenEnd"; }, never>;
@@ -103,6 +106,7 @@ export declare class MatChipInput implements MatChipTextControl, OnChanges {
 export interface MatChipInputEvent {
     input: HTMLInputElement;
     value: string;
+    clearInput(): void;
 }
 
 export declare class MatChipList extends _MatChipListMixinBase implements MatFormFieldControl<any>, ControlValueAccessor, AfterContentInit, DoCheck, OnInit, OnDestroy, CanUpdateErrorState {