doc: add conditional example for setBreakpoint()

The `node-inspect` debugging client supports passing an optional third
parameter as a string to be evaluated when the breakpoint is hit. If the
condition evaluates to `true` in the current context, the breakpoint
pauses execution; otherwise the execution continues.

This was raised as an issue in
https://github.com/nodejs/node-inspect/issues/68, but the client already
supports that functionality, so I thought it'd be helpful to add it to
the node documentation.

PR-URL: https://github.com/nodejs/node/pull/35823
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Jan Krems <jan.krems@gmail.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/doc/api/debugger.md b/doc/api/debugger.md
index 08664ff9677..89980cfbd4a 100644
--- a/doc/api/debugger.md
+++ b/doc/api/debugger.md
@@ -118,6 +118,9 @@ To begin watching an expression, type `watch('my_expression')`. The command
 functions body
 * `setBreakpoint('script.js', 1)`, `sb(...)`: Set breakpoint on first line of
 `script.js`
+* `setBreakpoint('script.js', 1, 'num < 4')`, `sb(...)`: Set conditional
+breakpoint on first line of `script.js` that only breaks when `num < 4`
+evaluates to `true`
 * `clearBreakpoint('script.js', 1)`, `cb(...)`: Clear breakpoint in `script.js`
 on line 1
 
@@ -145,6 +148,42 @@ break in mod.js:22
 debug>
 ```
 
+It is also possible to set a conditional breakpoint that only breaks when a
+given expression evaluates to `true`:
+
+```console
+$ node inspect main.js
+< Debugger listening on ws://127.0.0.1:9229/ce24daa8-3816-44d4-b8ab-8273c8a66d35
+< For help, see: https://nodejs.org/en/docs/inspector
+< Debugger attached.
+Break on start in main.js:7
+  5 }
+  6
+> 7 addOne(10);
+  8 addOne(-1);
+  9
+debug> setBreakpoint('main.js', 4, 'num < 0')
+  1 'use strict';
+  2
+  3 function addOne(num) {
+> 4   return num + 1;
+  5 }
+  6
+  7 addOne(10);
+  8 addOne(-1);
+  9
+debug> cont
+break in main.js:4
+  2
+  3 function addOne(num) {
+> 4   return num + 1;
+  5 }
+  6
+debug> exec('num')
+-1
+debug>
+```
+
 ### Information
 
 * `backtrace`, `bt`: Print backtrace of current execution frame