svelte.config.js

const sass = require("node-sass");
// This adds Language Server Protocol support for tools like vscode
// related: https://github.com/UnwrittenFun/svelte-vscode/issues/1

module.exports = {
  preprocess: {
    style: async ({ content, attributes }) => {
      if (
        !["text/sass", "text/scss"].some(attributes.type) &&
        !["sass", "scss"].some(attributes.lang)
      )
        return;

      return new Promise((resolve, reject) => {
        sass.render(
          {
            data: content,
            sourceMap: true,
            outFile: "x" // this is necessary, but is ignored
          },
          (err, result) => {
            if (err) return reject(err);

            resolve({
              code: result.css.toString(),
              map: result.map.toString()
            });
          }
        );
      });
    }
  }
};