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Can I install a NPM package from javascript running in Node.js?

Posted by: admin November 7, 2017 Leave a comment

Questions:

Can I install a NPM package from a javascript file running in Node.js? For example, I’d like to have a script, let’s call it “script.js” that somehow (…using NPM or not…) install a package usually available through NPM. In this example, I’d like to install “FFI”. (npm install ffi)

Answers:

It is indeed possible to use npm programmatically, and it was outlined in older revisions of the documentation. It has since been removed from the official documentation, but still exists on source control with the following statement:

Although npm can be used programmatically, its API is meant for use by
the CLI only, and no guarantees are made regarding its fitness for any
other purpose. If you want to use npm to reliably perform some task,
the safest thing to do is to invoke the desired npm command with
appropriate arguments.

The semantic version of npm refers to the CLI itself, rather than the
underlying API. The internal API is not guaranteed to remain stable
even when npm’s version indicates no breaking changes have been made
according to semver
.

In the original documentation, the following is the code sample that was provided:

var npm = require('npm')
npm.load(myConfigObject, function (er) {
  if (er) return handlError(er)
  npm.commands.install(['some', 'args'], function (er, data) {
    if (er) return commandFailed(er)
    // command succeeded, and data might have some info
  })
  npm.registry.log.on('log', function (message) { ... })
})

Since npm exists in the node_modules folder, you can use require('npm') to load it like any other module. To install a module, you will want to use npm.commands.install().

If you need to look in the source then it’s also on GitHub. Here’s a complete working example of the code, which is the equivalent of running npm install without any command-line arguments:

var npm = require('npm');
npm.load(function(err) {
  // handle errors

  // install module ffi
  npm.commands.install(['ffi'], function(er, data) {
    // log errors or data
  });

  npm.on('log', function(message) {
    // log installation progress
    console.log(message);
  });
});

Note that the first argument to the install function is an array. Each element of the array is a module that npm will attempt to install.

More advanced use can be found in the npm-cli.js file on source control.

Questions:
Answers:

yes. you can use child_process to execute a system command

var exec = require('child_process').exec,
    child;

 child = exec('npm install ffi',
 function (error, stdout, stderr) {
     console.log('stdout: ' + stdout);
     console.log('stderr: ' + stderr);
     if (error !== null) {
          console.log('exec error: ' + error);
     }
 });

Questions:
Answers:

if you want to have output as well you can use:

var child_process = require('child_process');
child_process.execSync("npm install ffi",{stdio:[0,1,2]});

this way you can watch the installation like you do it on hand and avoid bad surprises (buffer full, etc)

Questions:
Answers:

it can actually be a bit easy

var exec = require('child_process').exec;
child = exec('npm install ffi').stderr.pipe(process.stderr);

Questions:
Answers:

I had a heck of a time trying to get the first example to work inside a project directory, posting here in case anyone else finds this. As far as I can tell, NPM still works fine loaded directly, but because it assumes CLI, we have to repeat ourselves a little setting it up:

// this must come before load to set your project directory
var previous = process.cwd();
process.chdir(project);

// this is the part missing from the example above
var conf = {'bin-links': false, verbose: true, prefix: project}

// this is all mostly the same

var cli = require('npm');
cli.load(conf, (err) => {
    // handle errors
    if(err) {
        return reject(err);
    }

    // install module
    cli.commands.install(['ffi'], (er, data) => {
        process.chdir(previous);
        if(err) {
            reject(err);
        }
        // log errors or data
        resolve(data);
    });

    cli.on('log', (message) => {
        // log installation progress
        console.log(message);
    });
});

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