fix(drag-drop): prevent dragging selected text with the mouse

src/cdk/drag-drop/directives/drag.spec.ts

@@ -1132,6 +1132,34 @@ describe('CdkDrag', () => {
       subscription.unsubscribe();
     }));
 
+    it('should prevent the default `mousemove` action even before the drag threshold has ' +
+      'been reached', fakeAsync(() => {
+        const fixture = createComponent(StandaloneDraggable, [], 5);
+        fixture.detectChanges();
+        const dragElement = fixture.componentInstance.dragElement.nativeElement;
+
+        dispatchMouseEvent(dragElement, 'mousedown', 2, 2);
+        fixture.detectChanges();
+        const mousemoveEvent = dispatchMouseEvent(document, 'mousemove', 2, 2);
+        fixture.detectChanges();
+
+        expect(mousemoveEvent.defaultPrevented).toBe(true);
+      }));
+
+    it('should prevent the default `touchmove` action even before the drag threshold has ' +
+      'been reached', fakeAsync(() => {
+        const fixture = createComponent(StandaloneDraggable, [], 5);
+        fixture.detectChanges();
+        const dragElement = fixture.componentInstance.dragElement.nativeElement;
+
+        dispatchTouchEvent(dragElement, 'touchstart', 2, 2);
+        fixture.detectChanges();
+        const touchmoveEvent = dispatchTouchEvent(document, 'touchmove', 2, 2);
+        fixture.detectChanges();
+
+        expect(touchmoveEvent.defaultPrevented).toBe(true);
+      }));
+
   });
 
   describe('draggable with a handle', () => {

src/cdk/drag-drop/drag-ref.ts

@@ -525,6 +525,10 @@ export class DragRef<T = any> {
 
   /** Handler that is invoked when the user moves their pointer after they've initiated a drag. */
   private _pointerMove = (event: MouseEvent | TouchEvent) => {
+    // Prevent the default action as early as possible in order to block
+    // native actions like dragging the selected text or images with the mouse.
+    event.preventDefault();
+
     if (!this._hasStartedDragging) {
       const pointerPosition = this._getPointerPositionOnPage(event);
       const distanceX = Math.abs(pointerPosition.x - this._pickupPositionOnPage.x);
@@ -565,7 +569,6 @@ export class DragRef<T = any> {
 
     const constrainedPointerPosition = this._getConstrainedPointerPosition(event);
     this._hasMoved = true;
-    event.preventDefault();
     this._updatePointerDirectionDelta(constrainedPointerPosition);
 
     if (this._dropContainer) {