A task to inline workers

tasks/serialize-workers.js

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+const path = require('path');
+const babel = require('rollup-plugin-babel');
+const resolve = require('rollup-plugin-node-resolve');
+const common = require('rollup-plugin-commonjs');
+const rollup = require('rollup');
+const terser = require('rollup-plugin-terser').terser;
+const fse = require('fs-extra');
+
+async function build(input, {minify = true} = {}) {
+  const plugins = [
+    {
+      name: 'remove export let create',
+      transform(code, id) {
+        if (id !== input) {
+          return null;
+        }
+        return code.replace('export let create;\n', '');
+      }
+    },
+    common(),
+    resolve(),
+    babel({
+      'presets': [
+        [
+          '@babel/preset-env',
+          {
+            'modules': false,
+            'targets': 'last 2 version, not dead'
+          }
+        ]
+      ]
+    }),
+    {
+      name: 'serialize worker and export create function',
+      renderChunk(code) {
+        return `
+          const source = ${JSON.stringify(code)};
+          const blob = new Blob([source], {type: 'application/javascript'});
+          const url = URL.createObjectURL(blob);
+          export function create() {
+            return new Worker(url);
+          }
+        `;
+      }
+    }
+  ];
+
+  if (minify) {
+    plugins.push(terser());
+  }
+
+  const bundle = await rollup.rollup({input, plugins});
+  const {output} = await bundle.generate({format: 'es'});
+
+  if (output.length !== 1) {
+    throw new Error(`Unexpected output length: ${output.length}`);
+  }
+
+  const chunk = output[0];
+  if (chunk.isAsset) {
+    throw new Error('Expected a chunk, got an asset');
+  }
+
+  return chunk;
+}
+
+exports.build = build;
+
+
+/**
+ * Creates modules with inlined versions of the worker sources.  These modules
+ * export a `create` function for creating a worker.
+ */
+async function main() {
+  const inputDir = path.join(__dirname, '../src/ol/worker');
+  const outputDir = path.join(__dirname, '../build/ol/src/worker');
+
+  await fse.ensureDir(outputDir);
+
+  const entries = await fse.readdir(inputDir);
+  for (const entry of entries) {
+    if (!entry.endsWith('.js')) {
+      continue;
+    }
+
+    const chunk = await build(path.join(inputDir, entry));
+    await fse.writeFile(path.join(outputDir, entry), chunk.code);
+  }
+}
+
+if (require.main === module) {
+  main().catch(err => {
+    process.stderr.write(`${err.stack}\n`);
+    process.exit(1);
+  });
+}