Solving npm Usage of the –dev option is deprecated. Use –only=dev instead.


You want to install development dependencies for a NodeJS package using

npm install --dev

but you get this error message:

npm WARN install Usage of the `--dev` option is deprecated. Use `--only=dev` instead.


You can use

npm install # Install normal (not development) dependencies
npm install --only=dev # Install only development dependencies

instead. Note that npm install --only=dev will only install development dependencies, so in most cases you want to run both commands.

Posted by Uli Köhler in NodeJS

Using nodemon without a global installation


You want to use nodemon in order to automatically reload your NodeJS server, however you don’t want to require a global installation (npm install -g nodemon) but instead install it locally into the node_modules directory:


First, install nodemon as dependency (

npm install --save-dev nodemon

We installed it as development dependency for this example, but it will work just as well if you install it as a normal dependency using --save instead of --save-dev.

After that, add a script entry in package.json:

"scripts": {
  "devserver": "./node_modules/nodemon/bin/nodemon.js index.js"
}, /* rest of package.json */

Replace index.js with the name of the file you want to run using nodemon.

Now you can start the development server using

npm run devserver
Posted by Uli Köhler in NodeJS

How to use query string parameters in NodeJS request


You’re using the request library in order to make a HTTP GET request:

const request = require("request")

request.get("http://localhost:8000", function(err, response, body) {
    console.log(err, body);

Now you’re trying to add query parameters to the request. For this example, we’ll assume that you want to add one parameter: foo=bar


You can use the qs parameter like this:

const request = require("request")

request.get({url: "http://localhost:8000", qs: {"foo": "bar"}}, function(err, response, body) {
    console.log(err, body);

Note that just adding a qs parameter to request.get won’t work, you need to have a dictionary as first argument that contains at least {"url": <your URL>, "qs": {<one or multiple query parameters>}}

Credits to Daniel at StackOverflow

Posted by Uli Köhler in Javascript

Disabling SSL certificate checking in unirest (NodeJS)


You want to make a HTTP request with unirest like this:

const unirest = require('unirest');

but you encounter the following error:

{ error: 
   { Error: unable to verify the first certificate
       at TLSSocket.<anonymous> (_tls_wrap.js:1088:38)
       at emitNone (events.js:86:13)
       at TLSSocket.emit (events.js:188:7)
       at TLSSocket._finishInit (_tls_wrap.js:610:8)
       at TLSWrap.ssl.onhandshakedone (_tls_wrap.js:440:38) code: 'UNABLE_TO_VERIFY_LEAF_SIGNATURE' } }


You can work around this problem by using strictSSL(false) like this:

const unirest = require('unirest');


Note however that this might have negative effects on the security of your application as this request will be vulnerable to man-in-the-middle attacks.

Posted by Uli Köhler in Javascript

How to fix npm “Cannot find module ‘graceful-fs'” error


When running any npm command, you get a stacktrace similar to the following:

Error: Cannot find module 'graceful-fs'
at Function.Module._resolveFilename (module.js:338:15)
at Function.Module._load (module.js:280:25)
at Module.require (module.js:362:17)
at require (module.js:378:17)
at Object.<anonymous> (/usr/share/npm/lib/utils/ini.js:32:10)
   at Module._compile (module.js:449:26)
at Object.Module._extensions..js (module.js:467:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Module.require (module.js:362:17)

Continue reading →

Posted by Uli Köhler in NodeJS

How to get filesize in Node.js

To determine the size of a file in NodeJS (e.g. to get the size of myfile.txt) use fs.stat() or fs.statSync() like this:

const fs = require("fs"); //Load the filesystem module
const stats = fs.statSync("myfile.txt");
const fileSizeInBytes = stats.size;
//Convert the file size to megabytes (optional)
const fileSizeInMegabytes = fileSizeInBytes / 1000000.0;

Another option is to use the following function:

function getFilesizeInBytes(filename) {
    const stats = fs.statSync(filename);
    const fileSizeInBytes = stats.size;
    return fileSizeInBytes;


Posted by Uli Köhler in NodeJS