Use esbuild for building assets

assets/build.mjs

@@ -0,0 +1,63 @@
+// 2023-04-07
+//
+// This file does not work with esbuild > 0.16 as esbuild’s API has changed in
+// 0.17.
+//
+// esbuild-sass-plugin is pinned to version < 2.6 because versions > 2.5 require
+// esbuild 0.17.
+//
+// https://github.com/evanw/esbuild/blob/main/CHANGELOG.md#0170
+
+import esbuild from 'esbuild';
+import ElmPlugin from 'esbuild-plugin-elm';
+import { sassPlugin } from 'esbuild-sass-plugin';
+
+const args = process.argv.slice(2);
+const watch = args.includes('--watch');
+const deploy = args.includes('--deploy');
+
+const plugins = [
+  ElmPlugin({
+    cwd: './elm/',
+    debug: !deploy,
+    optimize: deploy,
+    clearOnWatch: watch,
+  }),
+  sassPlugin(),
+];
+
+let opts = {
+  entryPoints: ['js/app.js'],
+  bundle: true,
+  target: 'es2017',
+  outdir: '../priv/static/assets',
+  logLevel: 'info',
+  plugins,
+};
+
+if (watch) {
+  opts = {
+    ...opts,
+    watch,
+    sourcemap: 'inline',
+  };
+}
+
+if (deploy) {
+  opts = {
+    ...opts,
+    minify: true,
+  };
+}
+
+const promise = esbuild.build(opts);
+
+if (watch) {
+  promise.then((_result) => {
+    process.stdin.on('close', () => {
+      process.exit(0);
+    });
+
+    process.stdin.resume();
+  });
+}