Sass Asset Functions

Supplies a set of functions to Sass that keep physical asset location details out of your source code. Also allows one to define a cache-busting policy or specify asset hosts by url.

This module supplies functions to a Sass compiler which can be called from your Sass code. For example, the image-url used here in place of url adds build-time configuration to resolve the file to the proper location as seen from the web:

.some-selector {
  background-image: image-url('cat.jpg');
}

NB Please note that the functions option of dart-sass/node-sass is still experimental (>= v3.0.0).

Origin

This module provides some of the asset functions that came with Compass. Originally a fork of node-sass-asset-functions that was never merged.

Functions Exposed to Sass

• image-url($filename: null, $only_path: false)
• image-width($filename: null)
• image-height($filename: null)
• font-url($filename: null, $only-path: false)
• font-files($filenames...)
• inline-image($filename: null, $mime-type: null)

Usage

Basic usage is as easy as setting the functions property:

// non-module, require usage
const sass = require('sass');
const { default: assetFunctions } = require('@localnerve/sass-asset-functions');

const result = sass.compile(scss_filename, {
  functions: assetFunctions(/* options */)
  [, options...]
});

// module usage
import sass from 'sass';
import assetFunctions from '@localnerve/sass-asset-functions';

const result = sass.compile(scss_filename, {
  functions: assetFunctions(/* options */)
  [, options...]
});

Options

All options are optional.

| name | type | description | | --- | --- | --- | | sass | Object | A reference to an alternate Sass compiler to use other than dart-sass (must expose types). Defaults to undefined and a dart-sass reference is used | | images_path | String | The build-time file path to images. Defaults to public/images | | fonts_path | String | The build-time file path to fonts. Defaults to public/fonts | | http_images_path | String | The path to images as seen from the web (nothing to do with http). Defaults to /images | | http_fonts_path | String | The path to images as seen from the web (nothing to do with http). Defaults to /fonts | | asset_cache_buster | Function | Signature (http_path, real_path, callback(new_url)). Supply to perform url transform for image-url or font-url, presumably for asset cache busting, but useful for any change to the url path (before fragment) | | asset_host | Function | Signature (http_path, callback(new_url)). Supply to perform url transform for image-url or font-url, presumably to define an asset host, but useful for any change to the url before the path |

Examples

You can specify the paths to your resources using the following options (shown with defaults):

{
  images_path: 'public/images', // local directory
  fonts_path: 'public/fonts',
  http_images_path: '/images', // web path
  http_fonts_path: '/fonts'
}

So if your project images reside in public/img at build-time instead of public/images, you use it as follows:

const sass = require('sass');
const { default: assetFunctions } = require('@localnerve/sass-asset-functions');

const result = sass.compile(scss_filename, {
  functions: assetFunctions({
    images_path: 'public/img',
    http_images_path: '/images'
  })
  [, options...]
});

sass: Overriding the default compiler with Node-Sass

Example using the node-sass compiler using the new option sass.

const sass = require('node-sass');
const { default: assetFunctions } = require('@localnerve/sass-asset-functions');

const result = sass.compile(scss_filename, {
  functions: assetFunctions({ sass })
  [, options...]
});

asset_host: a function which completes with a string used as asset host.

const result = sass.compile(scss_filename, {
  functions: assetFunctions({
    asset_host: (http_path, done) => {
      done('http://assets.example.com');
      // or use the supplied path to calculate a host
      done(`http://assets${http_path.length % 4}.example.com`);
    }
  })
  [, options...]
});

asset_cache_buster: a function to rewrite the asset path

When this function returns a string, it's set as the query of the path. When returned an object, path and query will be used.

const result = sass.compile(scss_filename, {
  functions: assetFunctions({
    asset_cache_buster: (http_path, real_path, done) => {
      done('v=123');
    }
  })
  [, options...]
});

A more advanced example:

Here we include the file's hexdigest in the path, using the hexdigest module.

For example, /images/myimage.png would become /images/myimage-8557f1c9b01dd6fd138ba203e6a953df6a222af3.png.

const sass = require('sass');
const path = require('path');
const fs = require('fs');
const hexdigest = require('hexdigest');
const { default: assetFunctions } = require('@localnerve/sass-asset-functions');

const result = sass.compile(scss_filename, {
  functions: assetFunctions({
    asset_cache_buster: (http_path, real_path, done) => {
      hexdigest(real_path, 'sha1', (err, digest) => {
        if (err) {
          // an error occurred, maybe the file doesn't exist.
          // Calling `done` without arguments will result in an unmodified path.
          done();
        } else {
          const extname = path.extname(http_path);
          const basename = path.basename(http_path, extname);
          const new_name = `${basename}-${digest}${extname}`;
          done({path: path.join(path.dirname(http_path), new_name), query: null});
        }
      });
    }
  })
  [, options...]
});

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request