show flashing errors

index.html

@@ -112,9 +112,12 @@
                     return;
                 }
 
-                // flash file
+                // update progress
                 this.isFlashing = true;
                 this.progress = 0;
+
+                // flash file
+                try {
                     const flasher = new Nrf52DfuFlasher(serialPort);
                     await flasher.flash(file, (percentage) => {
                         this.progress = percentage;
@@ -123,6 +126,11 @@
                             alert("Firmware has been flashed!");
                         }
                     });
+                } catch(e) {
+                    this.isFlashing = false;
+                    alert("Firmware flashing failed: " + e);
+                    console.log(e);
+                }
 
             },
             async detect() {