I am working on an app wherein I would like to be able to install NPM modules via the frontend. I have no idea, though, how to do so. That is, I know how to do CRUD actions via the front end, but I don't know how to either interact with the command line or run command line functions via the front end.
Are there packages that can help with this or is this built into Node.js somehow?
In short, how can I connect my front-end to my backend in such a way that I can install an NPM package?
What you want is the child_process module. It's built-in so you don't need to install any additional module.
Mostly what you're looking for is either spawn() or exec().
For example, if you want to run npm install some_module you can do:
const { exec } = require('child_process');
let command = 'npm install some_module';
let options = { cwd: '/path/to/node/project' };
exec(command, options, (error, stdout, stderr) => {
// Do anything you want with program output here:
console.log('output:', stdout, stderr);
});
You may check the documentation for child_process in Node JS:
Child Process
const { spawn } = require('child_process');
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
The key difference between exec() and spawn() is how they return the data. As exec() stores all the output in a buffer, it is more memory intensive than spawn(), which streams the output as it comes.
Generally, if you are not expecting large amounts of data to be returned, you can use exec() for simplicity. Good examples of use-cases are creating a folder or getting the status of a file. However, if you are expecting a large amount of output from your command, then you should use spawn()
The easiest way to install an npm package via "the front end" is to have node spawn npm as a child process based off of the package name that the client provides.
var child = require('child_process').exec(`npm i ${package_name}`);
child.on('exit',function(){
//npm finished
});
This should install the module given that package_name is the name of the npm package, in the same directory that the script is running in. In terms of getting the package name from the front end to the back end, there are several different ways to do that.
You cannot run the your backend application without NPM modules installed, one thing that I think you can do is to make a plain nodejs file without any modules, which will receive the args when invoked, and you can use that args to the required modules, because that file will run with just core modules
I'm running the following code using node and I always get only about 80% of what stdout is supposed to return when the file is past 12ko or so. If the file is 240ko it will still output 80% of it. If it's under 12 it will output completely.
When I open a cmd and run the command manually I always get the full output.
I tried exec, execFile, I tried increasing the max buffer or changing the encoding and it's not the issue. I tried to add options {shell: true, detached: true} but it vain, in fact, when I run it as detached it seems to be running completely fine as it does open an actual console but I'm not able to retrieve the stdout when the process is completed.
const spawn = require('child_process').spawn;
const process = spawn(
'C:\\Users\\jeanphilipped\\Desktop\\unrtf\\test\\unrtf.exe',
['--html' ,'C:\\Users\\jeanphilipped\\Desktop\\unrtf\\test\\tempaf45.rtf'],
);
let chunks = [];
process.stdout.on('data', function (msg) {
chunks = [...chunks, ...msg];
});
process.on('exit', function (msg) {
const buffer = Buffer.from(chunks);
console.log(buffer.toString());
});
Any clues ? It seems to be Node since when I run it manually everything works fine.
according to nodejs documentation, all of the child_process commands are asynchronous . so when you try to access your chunk variable there is no guarantee that you command has been finished , maybe your command is still on process. so it is recommended you should wrap your entire child_process command in async/await function.
I'm building a command line interface in node which connects to a background command line daemon. If no daemon is running, the first time the cli is called it will fork off the daemon using child_process.fork
The daemon needs to launch instances of electron BrowserWindow, but requiring electron is showing unusual behavior.
If running the daemon on it's own in the foreground, everything works smoothly; however in the background I get an empty module when requiring electron.
Printing Object.keys(require('electron')) to console shows the number sequence 0..84, and printing the results of require('electron') shows the string /path/to/electron/dist/electron
Printing out process.argv shows that the forked script is definitely being executed with electron.
I'm stumped. Any direction would be greatly appreciated.
Example:
launcher
#!/usr/local/bin/electron
const cp = require('child_process');
console.log();
const cld = cp.fork(__dirname+'/daemon',{
stdio:['inherit','inherit','inherit','ipc']
});
cld.on('message', (code) => {
code = parseInt(code);
cld.disconnect();
process.exit(code);
});
daemon
#!/usr/local/bin/electron
const fs=require('fs');
const log = (x)=>fs.appendFileSync('log',x+'\n\n');
log('');
if(!process.send) process.send = console.log;
log(process.argv);
const e = require('electron');
log(e);
log(Object.keys(e));
log(e.app);
process.send(0);
Resulting log file
*removed*/lib/thirdparty/node_modules/electron/dist/electron,*removed*/tmp/daemon
*removed*/lib/thirdparty/node_modules/electron/dist/electron
0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84
undefined
Log file from running just daemon
*removed*/lib/thirdparty/node_modules/electron/dist/electron,./daemon
[object Object]
clipboard,nativeImage,shell,app,autoUpdater,BrowserView,BrowserWindow,contentTracing,crashReporter,dialog,globalShortcut,ipcMain,inAppPurchase,Menu,MenuItem,net,netLog,Notification,powerMonitor,powerSaveBlocker,protocol,screen,session,systemPreferences,TopLevelWindow,TouchBar,Tray,View,webContents,WebContentsView
[object App]
forked process by default set ELECTRON_RUN_AS_NODE=1 and will not expose any electron specific modules:
as https://github.com/electron/electron/issues/6656 says, you may need workaround by explicitly invoke process separately vice versa.
I am writing a CLI tool for a node.js app. Some of the commands have to run npm and show the results. This is what I have so far:
import {spawn} from 'child_process';
let projectRoot = '...';
let npm = (process.platform === "win32" ? "npm.cmd" : "npm"),
childProcess = spawn(npm, ["install"], { cwd: projectRoot });
childProcess.stdout.pipe(process.stdout);
childProcess.stderr.pipe(process.stderr);
childProcess.on('close', (code) => {
// Continue the remaining operations
});
The command does run fine and outputs the results (or errors). However, it doesn't give me a live feed with the progress bar, etc. It waits until the entire operation is over and then dumps the output into the console.
I've tried different variations of the spawn configuration but I can't get it to show me the live feed.
I am on Windows 10 and use node.js 4 and npm 3.
As discussed in the comments: Run the spawn with { stdio: 'inherit' }.
However, good question is why the 'manual piping' does not do the same. I think that's because npm uses the 'fancy progress bar'. It probably uses some special way how to deal with stdout that does not play well with process.stdout. If you try some other long-running command (such as 'find ./'), your way of piping works fine.
i am writing an utility. One command of this utility is to run an external application.
var child_process = require('child_process');
var fs = require('fs');
var out = fs.openSync('.../../log/out.log', 'a');
var err = fs.openSync('.../../log/err.log', 'a');
exports.Unref = function(app, argv) {
var child = child_process.spawn(app, argv, {
detached: true,
stdio: [ 'ignore', out, err ]
});
child.unref();
//process.exit(0);
};
Currently:
$ utility run app --some-args // run external app
// cant enter next command while app is running
My Problem is that if i run this command, the terminal is locked while the "external" Application is running.
But the terminal window shouldn't be locked by the child_process.
i wanna run:
$ utility run app --some-args
$ next-command
$ next-command
The external Application (a desktop application) will be closed by hisself.
Like this:
$ subl server.js // this runs Sublime Text and passes a file to the editor
$ npm start // The terminal does not locked - i can execute next command while Sublime is still running
You know what i mean ^^?
Appending ['>>../../log/out.log', '2>>../../log/err.log'] to the end of argv instead of leaving two files open should work since it's the open file handles that are keeping the process alive.
Passing opened file descriptors in stdio in addition to detached: true will not work the way you expect because there is no way to unref() the file descriptors in the parent process and have it still work for the child process. Even if there was a way, I believe that when the parent process exited, the OS would clean up (close) the file descriptors it had open, which would cause problems for the detached child process.
The only possible way that this might have been able to work would have been by passing file descriptors to child processes, but that functionality was dropped several stable branches ago because the same functionality did not exist on some other platforms (read: Windows).