How to disable in the node debugger "break on first line" - node.js

Is there a command line argument or an environment variable that disables the "break on first line" feature of the node debugger?

There are actually two debugger concepts in node: V8 debugger (with its TCP-based protocol) and a node command-line debugger (CLI).
When you run node debug app.js, a debugger CLI is run in the master node process and a new child node process is spawned for the debugged script (node --debug-brk app.js). The option --debug or --debug-brk is used to turn on V8 debugger in the child process.
The difference between --debug and --debug-brk is that the latter one adds a breakpoint on the first line, so that execution immediately stops there.
I would suggest you this solution:
When you are creating a child process from your webserver, run node --debug instead of node debug. This way there is only one child process created, it is running your application and it is not paused on the first line.
Now you can use any debugging tool that supports V8 debugger protocol - node built-in CLI debugger, node-inspector or you can event implement your own debugger front-end (GUI) if you like. (I presume this is what you are trying achieve by running CLI debugger in background?)
If you decided to use built-in CLI, just spawn another another child process and tell node CLI debugger to connect to the process started in step 1:
node debug localhost:5858
and continue as before.

According this issue I have opened in the node repo, currently, this is not possible. This is also something that the node guys don't see as a feature worth implementing "because it seems kind of pointless. […] Attaching to a running process does exactly" the same thing. See the rest of the discussion in the mentioned issue.
If you think you want such a feature, vote this up, leave a comment in the Github issue, and, if no response, open a new one and post it here as well.

Found this while looking for the answer myself - Seems that you can simply run
node-debug --debug-brk=0 (progname)
Hope this helps someone.

Write a chrome extension to click the start button
1. Run shell
mkdir run_as_devtools
cd run_as_devtools
touch manifest.json
touch run_as_devtools.js
2. Edit the files
run_as_devtools.js:
if (location.protocol === 'chrome-devtools:' && location.href.match(/ws=localhost/))(function () {
'use strict';
setTimeout(function () {
try {
document.querySelector('html /deep/ .long-click-glyph').click();
} catch (e) {
console.log(e);
}
}, 500);
})();
manifest.json: (it uses chromevox's key, so don't use it with chromevox)
{
"content_scripts": [{
"js": [ "run_as_devtools.js" ],
"matches": [ "<all_urls>" ]
}],
"key": "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDEGBi/oD7Yl/Y16w3+gee/95/EUpRZ2U6c+8orV5ei+3CRsBsoXI/DPGBauZ3rWQ47aQnfoG00sXigFdJA2NhNK9OgmRA2evnsRRbjYm2BG1twpaLsgQPPus3PyczbDCvhFu8k24wzFyEtxLrfxAGBseBPb9QrCz7B4k2QgxD/CwIDAQAB",
"manifest_version": 2,
"name": "Elevated Devtools extension",
"version": "1.0"
}
3. Install the extension
Chrome settings - More tools - Extensions- Developer mode - Load unpacked extension - select run_as_devtools folder
P.S. Better to use it with Node inspector manager https://stackoverflow.com/a/43018133/4831179
Reference: https://stackoverflow.com/a/17044405/4831179

I solved same issue just by switching from node v6 to v7

Similar to blackmiaool's idea but simpler, with node v8 you can start the script with --inspect. If you have the following code in it, when you open the debug window in Chrome devtools it will take you straight to the debugger point. Additionally this allows you to execute async code by hitting the "continue" button, which allows your code to run before returning you to the repl:
// app_shell.js
var UserModel = require("./some_user_model");
function looper() {
var Tmp = { UserModel: UserModel };
debugger;
setTimeout(looper, 100);
}
looper();
And in a shell script you can do something like:
echo "Click the 'Open dedicated DevTools for Node' link"
python -mwebbrowser about:inspect
node --inspect app_shell.js
See here for more info

This worked for me .
node --inspect index.js
If you haven't install inspector , install it as receommended by node docs:
npm install -g node-inspect

Related

How to disable warnings when node is launched via a (global) shell script

I am building a CLI tool with node, and want to use the fs.promise API. However, when the app is launched, there's always an ExperimentalWarning, which is super annoying and messes up with the interaction prompts. How can I disable this warning/all warnings?
I'm testing this with the latest node v10 lts release on Windows 10.
To use the CLI tool globally, I have added this to my package.json file:
{
//...
"preferGlobal": true,
"bin": { "myapp" : "./index.js" }
//...
}
And have run npm link to link the ./index.js script. Then I am able to run the app globally simply with myapp.
After some research I noticed that there are generally 2 ways to disable the warnings:
set environmental variable NODE_NO_WARNINGS=1
call the script with node --no-warnings ./index.js
Although I was able to disable the warnings with the 2 methods above, there seems to be no way to do that while directly running myapp command.
The shebang I placed in the entrance script ./index.js is:
#!/usr/bin/env node
// my code...
I have also read other discussions on modifying the shebang, but haven't found a universal/cross-platform way to do this - to either pass argument to node itself, or set the env variable.
If I publish this npm package, it would be great if there's a way to make sure the warnings of this single package are disabled in advance, instead of having each individual user tweak their environment themselves. Is there any hidden npm package.json configs that allow this?
Any help would be greatly appreciated!
I am now using a launcher script to spawn a child_process to work around this limitation. Ugly, but it works with npm link, global installs and whatnot.
#!/usr/bin/env node
const { spawnSync } = require("child_process");
const { resolve } = require("path");
// Say our original entrance script is `app.js`
const cmd = "node --no-warnings " + resolve(__dirname, "app.js");
spawnSync(cmd, { stdio: "inherit", shell: true });
As it's kind of like a hack, I won't be using this method next time, and will instead be wrapping the original APIs in a promise manually, sticking to util.promisify, or using the blocking/sync version of the APIs.
I configured my test script like this:
"scripts": {
"test": "tsc && cross-env NODE_OPTIONS=--experimental-vm-modules NODE_NO_WARNINGS=1 jest"
},
Notice the NODE_NO_WARNINGS=1 part. It disables the warnings I was getting from setting NODE_OPTIONS=--experimental-vm-modules
Here's what I'm using to run node with a command line flag:
#!/bin/sh
_=0// "exec" "/usr/bin/env" "node" "--experimental-repl-await" "$0" "$#"
// Your normal Javascript here
The first line tells the shell to use /bin/sh to run the script. The second line is a bit magical. To the shell it's a variable assignment _=0// followed by "exec" ....
Node sees it as a variable assignment followed by a comment - so it's almost a nop apart from the side effect of assigning 0 to _.
The result is that when the shell reaches line 2 it will exec node (via env) with any command line options you need.
New answer: You can also catch emitted warnings in your script and choose which ones to prevent from being logged
const originalEmit = process.emit;
process.emit = function (name, data, ...args) {
if (
name === `warning` &&
typeof data === `object` &&
data.name === `ExperimentalWarning`
//if you want to only stop certain messages, test for the message here:
//&& data.message.includes(`Fetch API`)
) {
return false;
}
return originalEmit.apply(process, arguments);
};
Inspired by this patch to yarn

NodeJS debug Starting inspector on 127.0.0.1:42457 failed: address already in use error

I am trying to debug my Discord bot using the DiscordJS lib. My trouble is that when I start a debug session (launching with vscode or with --inspect-brk | --debug-brk)
I get a Starting inspector on 127.0.0.1:42457 failed: address already in use error I have tried changing the port in both situations and still getting the same error on different ports. My bot is sharded so its start child process of itself. I have tried using vscode to attach to child processes but still the same error.
If anybody is familiar with DiscordJS and knows how to debug a sharded bot some help would be much appreciated
In my case to solve this, just add that config on nodemon.json
{
"execMap": {
"js": "node --inspect=9300 -r sucrase/register"
}
}
I added --inspect=9300 to set port to this specific port
First Ctrl C (or Cmd C) to quit all your progress in the cmd.
Start Task Manager > Find all tasks named "node" > End process.
Now go back to your cmd and start server.
That is because you are already running that application in with node filename.js, hence stop that process and start with debugging again with same port.
You can take a look that on the below video might help
https://www.youtube.com/watch?v=b8e9RAekktY&t=28s

VSCode - How to debug a Node program that starts its own debugger, using a launch configuration?

(Note : my specific use case may seem complex, but the underlying idea is not!)
I have a Gulp script that starts a Docker container, which itself contains and starts another Gulp script that use Nodemon to start a final Node script in debug mode! The Nodemon Gulp script ran inside the Docker container looks something like this :
nodemon({
"script": `start.js`,
"nodeArgs": [`--debug=0.0.0.0:5858`, "-nolazy"],
"ext": "js",
"restartable": true
});
I'd like to be able to press [F5] in Visual Studio Code, have the final script started and have VSCode's debugger attached to it!
What does work :
If I start the first Gulp script manually, in a terminal, the Docker container is started, the other embedded Gulp script with Nodemon is executed and the final script is started. I can then press [F5] in VSCode to start an attach launch configuration and I'm able to debug! The port 5858 is exposed by Docker and everything runs fine.
What I want :
I want to be able to skip the manual launching of the script in a terminal. I want a VSCode launch configuration that does everything by itself => launch the script in VSCode's integrated terminal and attach a debugger to the debug process started by the script itself.
I tried :
An "request": "attach" launch configuration with a preLaunchTask task. That task is launching the first Gulp script. The problem with this approach is that the preLaunchTask task never ends : it starts the first script in the terminal (The task has a : ""_runner": "terminal"") but in the end the final script is listening and doesn't exit (it's actually listening for requests)... This seems to prevent the VSCode debugger to start because the preLaunchTask task never exit.
A "request": "launch" launch configuration that starts the first script. But here, even if it looks like it is going to work (the orange debugging bar appears), the debugging never actually work. If I understand correctly, this is because a launch launch configuration starts a Node debugger by itself (on the specified port) and therefore the debugger starts by Nodemon, inside the Docker container, will never be listened to.
In other words : I simply want to hit [F5] so a script is launched in the integrated terminal, without debugger, and then VSCode will attach a debugger to the resulting 127.0.0.1:5858 debug process, wathever how this process is actually started.
UPDATE : I also had a suggestion on Github about trying to use a compound launch configuration, but it also doesn't work: https://github.com/Microsoft/vscode/issues/36685
Your first try, an attach config with a preLaunchTask is correct. You probably just need one adjustment. By default, vscode will be waiting for the task to terminate, so you need to tell it that the task will run in the background, by adding "isBackground": true. Then you need to tell it which patterns to watch for in the task's output to know when the task is complete. This bit is a little annoying, because you have to do this with a problemMatcher, but this task should not contribute problems, so you need to give it a regex that won't match anything. e.g.:
"problemMatcher": {
"pattern": {
"regexp": "__________"
},
"background": {
"activeOnStart": false,
"beginsPattern": "Some pattern when the debugging process is about to start",
"endsPattern": "Ready for attach"
}
}
The task runner is watching the program output to match endsPattern - when some output matches, then it will know the program is ready for the debugger to attach. If your script isn't producing any output, you should add some console.log after invoking nodemon.
Usually the problemMatcher is for matching problems output by the build task, and the regex can match the filename, line, and error message. But here we are just using it for the "background" patterns, so we give it a dummy regex. Here's a thread describing this workaround and how it could be easier in the future by moving the "background" patterns out of the patternMatcher:
https://github.com/Microsoft/vscode/issues/6209#issuecomment-289411630
And here is the documentation on watching tasks, for more details: https://code.visualstudio.com/docs/editor/tasks#_background-watching-tasks

How do I use node debug cli with Jest?

How can I just use the simple node cli/repl debugger with Jest?
The Jest documentation uses node-inspector, but it is outdated/deprecated as of Node 6.3. I tried the recommended command anyway on Node 7.7.4:
node --debug-brk ./node_modules/.bin/jest --runInBand --no-cache [your_test_file]
But this simply hangs on the following (assumedly waiting on node-inspector):
(node:13452) DeprecationWarning: node --debug is deprecated. Please use node --inspect instead. Debugger listening on 127.0.0.1:5858
I added --inspect as specified by the warning, but even then execution doesn't stop on my debugger statement in Chrome DevTools.
This seems overly complicated for a very simple use case.
I found the following command works:
node debug ./node_modules/.bin/jest --runInBand --no-cache [your_test_file]
...but with some quirky behavior. When the debugger first stops you will see:
break in node_modules/jest/bin/jest.js:10
8 */
9
>10 'use strict';
11
12 require('jest-cli/bin/jest');
debug>
Apparently Jest always injects this breakpoint so that you have time to open Chrome DevTools (irrelevant in our case since we're only going to use cli/repl).
Continue past this breakpoint with c, and after a short time (without any indication of course that things are progressing along) you should see your breakpoint:
break in webpack/assets/react/components/presentation/Feed/Comments/Comment/commentSpec.jsx:12
10 var wrapper = (0, _enzyme.shallow)(_react2.default.createElement(_comment2.default, { loading: true }));
11
>12 debugger;
13 expect(wrapper.find(_button2.default)).to.have.length(1);
14 });
debug>
The last weird thing is you need to type repl to inspect objects as described in Node Debugger and Inspecting variables using node's built-in debugger?
The combination of all these steps was not immediately obvious to me while reading the documentation, so I hope this answer helps someone get over the hurdle faster.
From node v8.4 the debugger keyword within the code is fixed for VM context. Refer this git comment.
1.Type debugger keyword in your Jest code:
describe('Testcase definition', () => {
it('should be defined with subobjects', () => {
debugger; // <-- This keyword breaks on Chrome inspect
expect(true).toBe(true);
});
});
Command to Run:
node --inspect-brk --inspect ./node_modules/.bin/jest -i tests/mytest.test.js
Now open chrome://inspect/#devices on Chrome. Voila!

VSCode debugging not working for NodeJs application

I have added the configuration in the launch.json file with the following details :
{
"name": "Attach"
"type": "node",
// TCP/IP address. Default is "localhost".
"address": "localhost",
// Port to attach to.
"port": 5858
}
Now I start my app with the following command : node --debug-brk ./bin/www
When i go to VSCode and select Attach in the debugging menu on the top and click on the play button.
It attaches, but when i go to browser and open a page, it doesn't it the breakpoint or the handler function in my index.js file.
Can you please help what could be going wrong?
There are two issues with breakpoints in node (and these issues are not specific to VSCode but you can see them in node-inspector as well):
If you set breakpoints in your app's startup code and launch node with --debug (opposed to --debug-brk), node starts immediately and has executed your startup code before VSCode had a chance to register the breakpoints. So if you need to debug startup code use the --debug-brk flag because it allows VSCode to set breakpoints before node starts the application.
Node does not parse source files completely on load but delays parsing of closures (callbacks etc.) until their code is first hit. As a consequence breakpoints set on callbacks are not always correctly registered by node, because it does not have parsed the code yet. This 'lazy' behaviour can be disabled by starting node with the --nolazy flag.
In the next version of VSCode (0.4.0) we try to address these problem as follows:
VScode will always launch node with the --debug-brk flag but will hide the first stop and continue if the user did not specify "stopOnEntry: true". This will avoid problems with missed breakpoints in startup code.
If breakpoints are set in code that has not been parsed by node, node will register them at the next possible position in parsed code. Since these "actual" positions are returned by node to the client, VSCode is able to show these positions. So the user will see that a breakpoint set in an unparsed callback "jumps" to a position further down and he will better understand why the debugger is not stopping at the location requested. In addition we added a "Reapply" button to the breakpoint view which makes it really easy to clear and set all breakpoints.
Your breakpoints are probably set too early and are not registered by node. It should help if you set the breakpoints after you have attached.
We have improved this experience in VSCode and it should be available in 0.4.0
Always clear your breakpoints and set them after you attach. I learned the hard way. This is certainly a bug.
I've been digging into this and here is what I have found so far for 0.3.0.
This does not work!
In Code add a breakpoint to app.js or a route
In terminal run node --debug src/server/app.js
In Code attach the debugger
This works!
In terminal run node --debug src/server/app.js
In Code remove all breakpoints
In Code add a breakpoint to app.js or a route
In Code attach the debugger
This does not work, as --debug doesn't kick in unless its the arg after node and before the file
In terminal run node src/server/app.js --debug
In Code remove all breakpoints
In Code add a breakpoint to app.js or a route
In Code attach the debugger
This works, assuming you have a gulp process
In terminal run gulp serve-dev --debug
In Code remove all breakpoints
In Code add a breakpoint to app.js or a route
In Code attach the debugger
This does not work, sometimes
In terminal run gulp serve-dev --debug
In Code add a breakpoint to app.js or a route
In Code attach the debugger
Why sometimes? The best I can tell is that that the breakpoints sometimes get funky. Sometimes they work fine, and other times I have to remove them and re-add them before attaching the debugger.

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