diff --git a/src/libs/gm.js b/src/libs/gm.js
new file mode 100644
index 0000000..c2a65ea
--- /dev/null
+++ b/src/libs/gm.js
@@ -0,0 +1,23 @@
+export const injectScript = ({ eventName }) => {
+  window.callGM = ({ action, args }, timeout = 5000) =>
+    new Promise((resolve, reject) => {
+      const handleEvent = (e) => {
+        window.removeEventListener(eventName + "_pong", handleEvent);
+        const { data, error } = e.detail;
+        if (error) {
+          reject(new Error(error));
+        } else {
+          resolve(data);
+        }
+      };
+
+      window.addEventListener(eventName + "_pong", handleEvent);
+      window.dispatchEvent(
+        new CustomEvent(eventName + "_ping", { action, args })
+      );
+
+      setTimeout(() => {
+        handleEvent({ detail: { error: "timeout" } });
+      }, timeout);
+    });
+};