Sapper postbuild Gulpfile

gulpfile.js

const tap = require('gulp-tap');
const postHTML = require('posthtml');
const { series, src, dest } = require('gulp');
const StreamFromPromise = require('stream-from-promise');
const { exec } = require('child_process');

const GLOB = './__sapper__/export/**/*.*';
const DEST = './__sapper__/rexport/';

const filter = (expr, cb) => file => expr.exec(file.path) && cb(file);

const runPostHtml = async file => {
  const { path, contents } = file;

  file.contents = StreamFromPromise(
    postHTML([
      // posthtml plugins goes here
    ])
      .process(contents)
      .then(({ html }) => html)
  );
};

const sapper = () => exec('sapper export --legacy');

exports.default = series(
  sapper,
  function html() {
    return src(GLOB)
      .pipe(tap(filter(/\.html?$/, runPostHtml)))
      .pipe(dest(DEST));
  }
);