inspector: add inspector.waitForDebugger()

This method blocks current node process until a client sends
Runtime.runifWaitingForDebugger.

It can be useful when we need to report inspector.url() before
waiting for connection:
```
inspector.open(0, undefined, false);
fs.writeFileSync(someFileName, inspector.url());
inspector.waitForDebugger();
```

PR-URL: https://github.com/nodejs/node/pull/28453
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>

2 files changed, 15 insertions, 0 deletions

diff --git a/doc/api/errors.md b/doc/api/errors.md
index fe81168e40..6147f768c8 100644
--- a/doc/api/errors.md
+++ b/doc/api/errors.md
@@ -1186,6 +1186,11 @@ after the session had already closed.
 
 An error occurred while issuing a command via the `inspector` module.
 
+<a id="ERR_INSPECTOR_NOT_ACTIVE"></a>
+### ERR_INSPECTOR_NOT_ACTIVE
+
+The `inspector` is not active when `inspector.waitForDebugger()` is called.
+
 <a id="ERR_INSPECTOR_NOT_AVAILABLE"></a>
 ### ERR_INSPECTOR_NOT_AVAILABLE
 
diff --git a/doc/api/inspector.md b/doc/api/inspector.md
index 63d2a70272..e2980a278d 100644
--- a/doc/api/inspector.md
+++ b/doc/api/inspector.md
@@ -52,6 +52,16 @@ parameter usage.
 
 Return the URL of the active inspector, or `undefined` if there is none.
 
+## inspector.waitForDebugger()
+<!-- YAML
+added: REPLACEME
+-->
+
+Blocks until a client (existing or connected later) has sent
+`Runtime.runIfWaitingForDebugger` command.
+
+An exception will be thrown if there is no active inspector.
+
 ## Class: inspector.Session
 
 The `inspector.Session` is used for dispatching messages to the V8 inspector