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doc: add information on suppressing initial break in debugger #40960

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Nov 26, 2021
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doc: add information on suppressing initial break in debugger #40960

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39 changes: 15 additions & 24 deletions doc/api/debugger.md
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Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,12 @@

<!-- type=misc -->

Node.js includes a command-line debugging utility. To use it, start Node.js
with the `inspect` argument followed by the path to the script to debug.
Node.js includes a command-line debugging utility. The Node.js debugger client
is not a full-featured debugger, but simple stepping and inspection are
possible.

To use it, start Node.js with the `inspect` argument followed by the path to the
script to debug.

```console
$ node inspect myscript.js
Expand All @@ -25,40 +29,26 @@ Break on start in myscript.js:2
debug>
```

The Node.js debugger client is not a full-featured debugger, but simple step and
inspection are possible.

Inserting the statement `debugger;` into the source code of a script will
enable a breakpoint at that position in the code:

<!-- eslint-disable no-debugger -->
The debugger automatically breaks on the first executable line. To instead
run until the first breakpoint (specified by a [`debugger`][] statement), set
the `NODE_INSPECT_RESUME_ON_START` environment variable to `1`.

```js
```console
$ cat myscript.js
// myscript.js
global.x = 5;
setTimeout(() => {
debugger;
console.log('world');
}, 1000);
console.log('hello');
```

Once the debugger is run, a breakpoint will occur at line 3:

```console
$ node inspect myscript.js
< Debugger listening on ws://127.0.0.1:9229/621111f9-ffcb-4e82-b718-48a145fa5db8
$ NODE_INSPECT_RESUME_ON_START=1 node inspect myscript.js
< Debugger listening on ws://127.0.0.1:9229/f1ed133e-7876-495b-83ae-c32c6fc319c2
< For help, see: https://nodejs.org/en/docs/inspector
<
connecting to 127.0.0.1:9229 ... ok
< Debugger attached.
<
ok
Break on start in myscript.js:2
1 // myscript.js
> 2 global.x = 5;
3 setTimeout(() => {
4 debugger;
debug> cont
< hello
<
break in myscript.js:4
Expand Down Expand Up @@ -252,5 +242,6 @@ Chrome DevTools doesn't support debugging [worker threads][] yet.
[ndb][] can be used to debug them.

[Chrome DevTools Protocol]: https://chromedevtools.github.io/devtools-protocol/
[`debugger`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/debugger
[ndb]: https://github.com/GoogleChromeLabs/ndb/
[worker threads]: worker_threads.md