The solution to this issue has been explained in other threads, see: How to compile scss to css with node-sass

However, here's my solution using the run-watch program, nodemon:

npm install node-sass nodemon --save-dev

In package.json, add these to your "scripts":

 "build-css": "node-sass --include-path scss src/input.scss src/styles.css",
 "watch-css": "nodemon -e scss -x \"npm run build-css\" "

Then, in your "start" script, use this:

 "start": "concurrently \"node app.js\" \"npm run watch-css\" "

Next, we need to install the concurrently package:

npm install concurrently --save

To compile and serve your files,

npm start

Therefore, the "npm start" command triggers a build that starts the app and concurrently calls the "run watch-css" command which in turn calls "build-css" to compile scss to css in real-time through nodemon. It compiles and refreshes live when you edit any scss in your text editor.

I picked node-sass implementer for libsass because it is based on node.js.

Installing node-sass

• (Prerequisite) If you don't have npm, install Node.js first.
• $ npm install -g node-sass installs node-sass globally -g.

This will hopefully install all you need, if not read libsass at the bottom.

How to use node-sass from Command line and npm scripts

General format:

$ node-sass [options] <input.scss> [output.css]
$ cat <input.scss> | node-sass > output.css

Examples:

1. $ node-sass my-styles.scss my-styles.css compiles a single file manually.
2. $ node-sass my-sass-folder/ -o my-css-folder/ compiles all the files in a folder manually.
3. $ node-sass -w sass/ -o css/ compiles all the files in a folder automatically whenever the source file(s) are modified. -w adds a watch for changes to the file(s).

More usefull options like 'compression' @ here. Command line is good for a quick solution, however, you can use task runners like Grunt.js or Gulp.js to automate the build process.

You can also add the above examples to npm scripts. To properly use npm scripts as an alternative to gulp read this comprehensive article @ css-tricks.com especially read about grouping tasks.

• If there is no package.json file in your project directory running $ npm init will create one. Use it with -y to skip the questions.
• Add "sass": "node-sass -w sass/ -o css/" to scripts in package.json file. It should look something like this:

"scripts": {
    "test" : "bla bla bla",
    "sass": "node-sass -w sass/ -o css/"
 }

• $ npm run sass will compile your files.

How to use with gulp

• $ npm install -g gulp installs Gulp globally.
• If there is no package.json file in your project directory running $ npm init will create one. Use it with -y to skip the questions.
• $ npm install --save-dev gulp installs Gulp locally. --save-dev adds gulp to devDependencies in package.json.
• $ npm install gulp-sass --save-dev installs gulp-sass locally.
• Setup gulp for your project by creating a gulpfile.js file in your project root folder with this content:

'use strict';
var gulp = require('gulp');

A basic example to transpile

Add this code to your gulpfile.js:

var gulp = require('gulp');
var sass = require('gulp-sass');
gulp.task('sass', function () {
  gulp.src('./sass/**/*.scss')
    .pipe(sass().on('error', sass.logError))
    .pipe(gulp.dest('./css'));
});

$ gulp sass runs the above task which compiles .scss file(s) in the sass folder and generates .css file(s) in the css folder.

To make life easier, let's add a watch so we don't have to compile it manually. Add this code to your gulpfile.js:

gulp.task('sass:watch', function () {
  gulp.watch('./sass/**/*.scss', ['sass']);
});

All is set now! Just run the watch task:

$ gulp sass:watch

How to use with Node.js

As the name of node-sass implies, you can write your own node.js scripts for transpiling. If you are curious, check out node-sass project page.

What about libsass?

Libsass is a library that needs to be built by an implementer such as sassC or in our case node-sass. Node-sass contains a built version of libsass which it uses by default. If the build file doesn't work on your machine, it tries to build libsass for your machine. This process requires Python 2.7.x (3.x doesn't work as of today). In addition:

LibSass requires GCC 4.6+ or Clang/LLVM. If your OS is older, this version may not compile. On Windows, you need MinGW with GCC 4.6+ or VS 2013 Update 4+. It is also possible to build LibSass with Clang/LLVM on Windows.