Only listen to process exit event once.

Also, stop performing an asynchronous action on process exit. It is not officially supported. However subprocess.kill is not asynchronous, so can be used over the internal killProcess method.

Fixes bubenshchykov#239. Should help bubenshchykov#231. Supersedes bubenshchykov#179

Author: philnash

src/process.js

@@ -72,8 +72,6 @@ async function startProcess(opts) {
     activeProcess = null;
   });
 
-  process.on("exit", async () => await killProcess());
-
   try {
     const url = await apiUrl;
     activeProcess = ngrok;
@@ -91,13 +89,21 @@ async function startProcess(opts) {
 }
 
 function killProcess() {
-  if (!activeProcess) return;
+  if (!activeProcess) {
+    return Promise.resolve();
+  }
   return new Promise((resolve) => {
     activeProcess.on("exit", () => resolve());
     activeProcess.kill();
   });
 }
 
+process.on("exit", () => {
+  if (activeProcess) {
+    activeProcess.kill();
+  }
+});
+
 /**
  * @param {string | Ngrok.Options} optsOrToken
  */