fix: prevent multiply pointers drawing

src/signature_pad.ts

@@ -187,7 +187,11 @@ export default class SignaturePad extends SignatureEventTarget {
   public on(): void {
     // Disable panning/zooming when touching canvas element
     this.canvas.style.touchAction = 'none';
-    (this.canvas.style as CSSStyleDeclaration & { msTouchAction: string | null }).msTouchAction = 'none';
+    (
+      this.canvas.style as CSSStyleDeclaration & {
+        msTouchAction: string | null;
+      }
+    ).msTouchAction = 'none';
     this.canvas.style.userSelect = 'none';
 
     const isIOS =
@@ -211,7 +215,11 @@ export default class SignaturePad extends SignatureEventTarget {
   public off(): void {
     // Enable panning/zooming when touching canvas element
     this.canvas.style.touchAction = 'auto';
-    (this.canvas.style as CSSStyleDeclaration & { msTouchAction: string | null }).msTouchAction = 'auto';
+    (
+      this.canvas.style as CSSStyleDeclaration & {
+        msTouchAction: string | null;
+      }
+    ).msTouchAction = 'auto';
     this.canvas.style.userSelect = 'auto';
 
     this.canvas.removeEventListener('pointerdown', this._handlePointerDown);
@@ -225,7 +233,7 @@ export default class SignaturePad extends SignatureEventTarget {
     const canvasWindow =
       window.document === this.canvas.ownerDocument
         ? window
-        : this.canvas.ownerDocument.defaultView ?? this.canvas.ownerDocument;
+        : (this.canvas.ownerDocument.defaultView ?? this.canvas.ownerDocument);
 
     return {
       addEventListener: canvasWindow.addEventListener.bind(
@@ -376,7 +384,11 @@ export default class SignaturePad extends SignatureEventTarget {
   };
 
   private _handlePointerDown = (event: PointerEvent): void => {
-    if (!this._isLeftButtonPressed(event) || this._drawingStroke) {
+    if (
+      !event.isPrimary ||
+      !this._isLeftButtonPressed(event) ||
+      this._drawingStroke
+    ) {
       return;
     }
 
@@ -386,7 +398,11 @@ export default class SignaturePad extends SignatureEventTarget {
   };
 
   private _handlePointerMove = (event: PointerEvent): void => {
-    if (!this._isLeftButtonPressed(event, true) || !this._drawingStroke) {
+    if (
+      !event.isPrimary ||
+      !this._isLeftButtonPressed(event, true) ||
+      !this._drawingStroke
+    ) {
       // Stop when primary button not pressed or multiple buttons pressed
       this._strokeEnd(this._pointerEventToSignatureEvent(event), false);
       return;