fix(badge): hide badges with no content (#12239)

Author: crisbeto

src/lib/badge/badge.spec.ts

@@ -114,6 +114,32 @@ describe('MatBadge', () => {
     expect(badgeContent.getAttribute('aria-describedby')).toBeFalsy();
   });
 
+  it('should toggle visibility based on whether the badge has content', () => {
+    const classList = badgeNativeElement.classList;
+
+    expect(classList.contains('mat-badge-hidden')).toBe(false);
+
+    testComponent.badgeContent = '';
+    fixture.detectChanges();
+
+    expect(classList.contains('mat-badge-hidden')).toBe(true);
+
+    testComponent.badgeContent = 'hello';
+    fixture.detectChanges();
+
+    expect(classList.contains('mat-badge-hidden')).toBe(false);
+
+    testComponent.badgeContent = ' ';
+    fixture.detectChanges();
+
+    expect(classList.contains('mat-badge-hidden')).toBe(true);
+
+    testComponent.badgeContent = 0;
+    fixture.detectChanges();
+
+    expect(classList.contains('mat-badge-hidden')).toBe(false);
+  });
+
 });
 
 /** Test component that contains a MatBadge. */
@@ -132,7 +158,7 @@ describe('MatBadge', () => {
 })
 class BadgeTestApp {
   badgeColor: ThemePalette;
-  badgeContent = '1';
+  badgeContent: string | number = '1';
   badgeDirection = 'above after';
   badgeHidden = false;
   badgeSize = 'medium';

src/lib/badge/badge.ts

@@ -31,10 +31,12 @@ export type MatBadgeSize = 'small' | 'medium' | 'large';
     '[class.mat-badge-small]': 'size === "small"',
     '[class.mat-badge-medium]': 'size === "medium"',
     '[class.mat-badge-large]': 'size === "large"',
-    '[class.mat-badge-hidden]': 'hidden',
+    '[class.mat-badge-hidden]': 'hidden || !_hasContent',
   },
 })
 export class MatBadge implements OnDestroy {
+  /** Whether the badge has any content. */
+  _hasContent = false;
 
   /** The color of the badge. Can be `primary`, `accent`, or `warn`. */
   @Input('matBadgeColor')
@@ -62,8 +64,9 @@ export class MatBadge implements OnDestroy {
   /** The content for the badge */
   @Input('matBadge')
   get content(): string { return this._content; }
-  set content(val: string) {
-    this._content = val;
+  set content(value: string) {
+    this._content = value;
+    this._hasContent = value != null && `${value}`.trim().length > 0;
     this._updateTextContent();
   }
   private _content: string;