Update gulp to v4

gulpfile.js

@@ -0,0 +1,75 @@
+'use strict';
+
+const gulp = require('gulp');
+
+const NODE_SRC = './src/**/*.js';
+const NODE_DEST = './lib';
+
+const cli = require('commander')
+  .usage('<task> [options]')
+  .option('-e, --env <environment>', 'Can be `prod` or `dev`. Default is `dev`', /^(dev|prod)$/, 'dev')
+  .option('-a, --analyze', 'Analyze client bundle. If set, `env` will be set to `prod`.')
+  .parse(process.argv);
+
+let watching = false;
+const task = cli.args[0] || 'watch';
+if (task === 'build' || cli.analyze) {
+  cli.env = 'prod';
+}
+
+gulp.task('clean', gulp.parallel(cleanNodeScripts, cleanViewerScripts));
+gulp.task('build', gulp.series('clean', compileNodeScripts, compileViewerScripts));
+gulp.task('watch', gulp.series('build', watch));
+gulp.task('default', gulp.task('watch'));
+
+function watch() {
+  watching = true;
+  gulp.watch(NODE_SRC, gulp.series(cleanNodeScripts, compileNodeScripts));
+}
+
+function cleanViewerScripts() {
+  const del = require('del');
+  return del('public');
+}
+
+function cleanNodeScripts() {
+  const del = require('del');
+  return del(NODE_DEST);
+}
+
+function compileNodeScripts() {
+  const babel = require('gulp-babel');
+  const plumber = require('gulp-plumber');
+  const noop = require('gulp-noop');
+
+  return gulp
+    .src(NODE_SRC)
+    .pipe(watching ? plumber() : noop())
+    .pipe(babel())
+    .pipe(gulp.dest(NODE_DEST));
+}
+
+function compileViewerScripts() {
+  const webpack = require('webpack');
+  const config = require('./webpack.config')({
+    env: cli.env,
+    analyze: cli.analyze
+  });
+
+  return new Promise((resolve, reject) => {
+    webpack(config, (err, stats) => {
+      if (cli.env === 'dev') {
+        if (err) {
+          console.error(err);
+        } else {
+          console.log(stats.toString({ colors: true }));
+        }
+        resolve();
+      } else {
+        if (err) return reject(err);
+        console.log(stats.toString({ colors: true }));
+        resolve();
+      }
+    });
+  });
+}

package.json

@@ -62,11 +62,10 @@
     "eslint": "3.19.0",
     "eslint-plugin-react": "7.0.0",
     "exports-loader": "0.6.4",
-    "gulp": "3.9.1",
-    "gulp-babel": "6.1.2",
+    "gulp": "4.0.0",
+    "gulp-babel": "7.0.1",
+    "gulp-noop": "1.0.0",
     "gulp-plumber": "1.2.0",
-    "gulp-util": "3.0.8",
-    "gulp-watch": "5.0.0",
     "mocha": "5.0.0",
     "nightmare": "2.10.0",
     "preact": "8.2.7",