Merge pull request #9946 from IgniteUI/mpopov/disabled-button

fix(button): Make IgxButtonDirective to work with disabled attr

Author: zdrawku

projects/igniteui-angular/src/lib/directives/button/button.directive.ts

@@ -238,7 +238,7 @@ export class IgxButtonDirective extends DisplayDensityBase {
      */
     @Input()
     @HostBinding('class.igx-button--disabled')
-    public get disabled() {
+    public get disabled(): boolean {
         return this._disabled;
     }
 
@@ -251,7 +251,7 @@ export class IgxButtonDirective extends DisplayDensityBase {
      * ```
      */
     public set disabled(val: boolean) {
-        this._disabled = !!val;
+        this._disabled = (val as any === '') || val;
     }
 
     /**

src/app/button/button.sample.html

@@ -12,7 +12,7 @@ <h4 class="sample-title">Flat Buttons</h4>
                 <input type="button" igxButton="flat" igxRipple="white" value="Input" />
             </div>
             <div class="button-sample">
-                <button igxButton="flat" [disabled]="true">Flat</button>
+                <button igxButton="flat" disabled>native disabled</button>
             </div>
             <div class="button-sample red-sox-button">
                 <button igxButton="flat" [disabled]="true">Red Sox</button>