Don't mutate the actual state object. (#49)

Fixes #45

Author: microbit-matt-hillsdon

src/demo.html

@@ -92,7 +92,9 @@ <h1>MicroPython-micro:bit simulator example embedding</h1>
               <option value="pin_logo">Pin logo</option>
               <option value="radio">Radio</option>
               <option value="sensors">Sensors</option>
-              <option value="sound_effects_builtin">Sound effects (builtin)</option>
+              <option value="sound_effects_builtin">
+                Sound effects (builtin)
+              </option>
               <option value="sound_effects_user">Sound effects (user)</option>
               <option value="speech">Speech</option>
               <option value="volume">Volume</option>
@@ -319,9 +321,10 @@ <h1>MicroPython-micro:bit simulator example embedding</h1>
           const labelElt = document.createElement("label");
           const text = labelElt.appendChild(document.createElement("span"));
           text.innerText = info.type;
-          delete info.type;
           const infoText = labelElt.appendChild(document.createElement("code"));
-          infoText.innerText = JSON.stringify(info);
+          const infoMutable = { ...info };
+          delete infoMutable.type;
+          infoText.innerText = JSON.stringify(infoMutable);
           return labelElt;
         };