fix: Add null check in destroy() before disconnecting sensor (#21)

* fix: Add null check in destroy() before disconnecting sensor

Fixes a TypeError that occurs when sensor.disconnect() is called
  on an already destroyed sensor during React StrictMode's double
  mount/unmount cycle.

  The destroy() function attempted to call sensor.disconnect()
  without checking if sensor was still defined, leading to:
  "TypeError: Cannot read properties of undefined (reading 'disconnect')"

  This commonly occurs in React 18+ StrictMode environments where
  components are intentionally mounted and unmounted twice to detect
  side effects, causing multiple destroy() calls on the same sensor.

* Bump version from 1.0.2 to 1.0.3

---------

Co-authored-by: hustcc <[email protected]>

Author: bluems

package.json

@@ -1,6 +1,6 @@
 {
   "name": "size-sensor",
-  "version": "1.0.2",
+  "version": "1.0.3",
   "description": "DOM element size sensor which will callback when size changed.",
   "main": "lib/index.js",
   "types": "index.d.ts",

src/sensors/resizeObserver.js

@@ -53,7 +53,9 @@ export const createSensor = (element, whenDestroy) => {
    * destroy
    */
   const destroy = () => {
-    sensor.disconnect();
+    if (sensor) {
+      sensor.disconnect();
+    }
 
     listeners = [];
     sensor = undefined;