How to compile .less files on save in Visual Studi

Question

Ok, so I've created a new ASP.Net 5/MVC 6 project in Visual Studio 2015 Preview. In keeping with our current method of doing things, for styling I want to use .less files. Creating the files is straightforward, but Web Essentials no longer compiles them.

So my question is this: what precisely do I need to do to get my .css files generated when I save the .less files?

Based on my adventures getting Typescript to work nicely, I will have to use Grunt to accomplish this task, but I am brand-new to Grunt and so I'm not sure how one would do it?

Please help!

Answer 1

With VS 2015 Web Essential is split into multiple extensions you can download the Web Compiler extension from here and it also has details on how to use it.

It is certainly not elegant as it used to be, but if you are using existing project and want to use a compiler for LESS then this may do the basic job.

Answer 2

So here's how to do it (compile on build and non-elegant compile on save):

Step 1

Open up your package.json file (it's in the root of your project) and add these lines:

"grunt-contrib-less": "^1.0.0",
"less": "^2.1.2"

Obviously you can change the version numbers (you'll get helpful intellisense), these are just the current versions.

Step 2

Right-click on the NPM folder (under Dependencies) and click Restore Packages. This will install less and grunt-contrib-less.

Step 3

Once those packages are restored, go to your gruntfile.js file (again, in the root of the project). Here, you'll need to add the following section to grunt.initConfig

less: {
    development: {
        options: {
            paths: ["importfolder"]
        },
        files: {
            "wwwroot/destinationfolder/destinationfilename.css": "sourcefolder/sourcefile.less"
        }
    }
}

You'll also need to add this line near the end of gruntfile.js:

grunt.loadNpmTasks("grunt-contrib-less");

Step 4

Then just go to View->Other Windows->Task Runner Explorer in the menu hit the refresh icon/button, then right-click on less under Tasks and go to Bindings and tick After Build.

Hooray, now less files will compile and we (I) learned about grunt, which seems really powerful.

Step 5: Compiling on save

I still haven't got this working to my satisfaction, but here's what I've got so far:

As above, add another NPM package grunt-contrib-watch (add to package.json, then restore packages).

Then add a watch section in gruntfile.js, like this (obviously this can work for other types of files as well):

watch: {
    less: {
        files: ["sourcefolder/*.less"],
        tasks: ["less"],
        options: {
            livereload: true
        }
    }
}

So you'll now have something like this in your gruntfile.js:

/// <binding AfterBuild='typescript' />
// This file in the main entry point for defining grunt tasks and using grunt plugins.
// Click here to learn more. http://go.microsoft.com/fwlink/?LinkID=513275&clcid=0x409

module.exports = function (grunt) {
    grunt.initConfig({
        bower: {
            install: {
                options: {
                    targetDir: "wwwroot/lib",
                    layout: "byComponent",
                    cleanTargetDir: false
                }
            }
        },
        watch: {
            less: {
                files: ["less/*.less"],
                tasks: ["less"],
                options: {
                    livereload: true
                }
            }
        },
        less: {
            development: {
                options: {
                    paths: ["less"]
                },
                files: {
                    "wwwroot/css/style.css": "less/style.less"
                }
            }
        }
    });

    // This command registers the default task which will install bower packages into wwwroot/lib
    grunt.registerTask("default", ["bower:install"]);

    // The following line loads the grunt plugins.
    // This line needs to be at the end of this this file.
    grunt.loadNpmTasks("grunt-bower-task");
    grunt.loadNpmTasks("grunt-contrib-less");
    grunt.loadNpmTasks("grunt-contrib-watch");
};

One can then simply set this task to run on Project Open (right-click on watch under Tasks in the Task Runner Explorer (it's under View->Other Windows in the top menu) and you're done. I would expect you'd have to close and re-open the project/solution to get this to kick in, otherwise you can manually run the task.

Answer 3

(Note: there is now a new question asked here directly concerning sass. I tried to alter the question and tags in this question to include sass, but someone didn't allow it.)

I would like to add the answer to the same question for sass (.scss). The answer is so related I think these may best be combined as two answers in this same post (if you disagree, please let me know; else, we might add "or sass" in the post title?). As such, see Maverick's answer for some fuller details, here's the nutshell for sass:

(Pre-step for Empty Projects) If you started with an empty project, first add Grunt and Bower:

Right click solution -> Add -> 'Grunt and Bower to Project' (then wait for a minute for it to all install)

package.json:

"devDependencies": {
    "grunt": "^0.4.5",
    "grunt-bower-task": "^0.4.0",
    "grunt-contrib-watch": "^0.6.1",
    "grunt-contrib-sass": "^0.9.2"
}

(FYI: grunt-contrib-sass link)

Then:

Dependencies -> right-click NPM -> Restore Packages.

gruntfile.js

1) Add or make sure these three lines are registered near the bottom (as NPM tasks):

grunt.loadNpmTasks("grunt-bower-task");
grunt.loadNpmTasks("grunt-contrib-watch");
grunt.loadNpmTasks("grunt-contrib-sass");

2) Again in gruntfile.js, add init configurations, something like the following.

{ Caveat: I am no expert on such configurations. I found the sass configuration on an excellent blog post some time ago that I can't locate at this time in order to give credit. The key was I wanted to find all files in the project within a certain folder (plus descendants). The following does that (notice "someSourceFolder/**/*.scss", and see important related note here). }

// ... after bower in grunt.initConfig ...
"default": {
    "files": [
        {
            "expand": true,
            "src": [ "someSourceFolder/**/*.scss" ],
            "dest": "wwwroot/coolbeans", // or "<%= src %>" for output to the same (source) folder
            "ext": ".css"
        }
    ]
},
"watch": {
    "sass": {
        "files": [ "someSourceFolder/**/*.scss" ],
        "tasks": [ "sass" ],
        "options": {
            "livereload": true
        }
    }
}

Now follow the instructions for Task Runner Explorer as given in the other answer. Make sure to close and reopen project. It seems you have to run (double click) 'watch' (under 'Tasks') every time the project is started to get the watch watching, but then it works on subsequent saves.