Simplify _startupCallback by passing callback rather than ID.

packages/accounts-base/accounts_client.js

@@ -441,16 +441,14 @@ export class AccountsClient extends AccountsCommon {
   // at registration time if already logged in
   // this can happen when new AccountsClient is created
   // before callbacks are registered see #10157
-  _startupCallback(callbackId) {
+  _startupCallback(callback) {
     // Are we already logged in?
     if (this.connection._userId) {
-      // Then go ahead and call the callback that we just registered.
-      const cb = this._onLoginHook.callbacks[callbackId];
       // If already logged in before handler is registered, it's safe to
-      // assume type is a 'resume', and execute the callback at the end of
-      // the queue so that Meteor.startup can complete before any embedded
-      // onLogin callbacks would execute.
-      Meteor.setTimeout(() => cb({ type: 'resume' }), 0);
+      // assume type is a 'resume', so we execute the callback at the end
+      // of the queue so that Meteor.startup can complete before any
+      // embedded onLogin callbacks would execute.
+      Meteor.setTimeout(() => callback({ type: 'resume' }), 0);
     }
   }
 

packages/accounts-base/accounts_common.js

@@ -198,7 +198,7 @@ export class AccountsCommon {
   onLogin(func) {
     let ret = this._onLoginHook.register(func);
     // call the just registered callback if already logged in
-    this._startupCallback(this._onLoginHook.nextCallbackId - 1);
+    this._startupCallback(ret.callback);
     return ret;
   }
 
@@ -289,8 +289,8 @@ export class AccountsCommon {
     return new Date() > (new Date(when) - minLifetimeMs);
   }
 
-  // noop on the server overridden on the client
-  _startupCallback(callbackId) {}
+  // No-op on the server, overridden on the client.
+  _startupCallback(callback) {}
 }
 
 // Note that Accounts is defined separately in accounts_client.js and

packages/accounts-base/package.js

@@ -1,6 +1,6 @@
 Package.describe({
   summary: "A user account system",
-  version: "1.4.4",
+  version: "1.4.5",
 });
 
 Package.onUse(api => {

packages/callback-hook/hook.js

@@ -77,6 +77,7 @@ export class Hook {
     this.callbacks[id] = callback;
 
     return {
+      callback,
       stop: () => {
         delete this.callbacks[id];
       }

packages/callback-hook/package.js

@@ -1,6 +1,6 @@
 Package.describe({
   summary: "Register callbacks on a hook",
-  version: '1.1.0'
+  version: '1.2.0'
 });
 
 Package.onUse(function (api) {