add functions for making npm rollup configs

Author: lobsterkatie

rollup/index.js

@@ -5,4 +5,5 @@ import * as plugins from './plugins/index.js';
 export { plugins };
 
 export * from './bundleHelpers.js';
+export * from './npmHelpers.js';
 export { insertAt } from './utils.js';

rollup/npmHelpers.js

@@ -0,0 +1,70 @@
+/**
+ * Rollup config docs: https://rollupjs.org/guide/en/#big-list-of-options
+ */
+
+import { builtinModules } from 'module';
+import * as path from 'path';
+
+import deepMerge from 'deepmerge';
+
+import { makeNodeResolvePlugin, makeSucrasePlugin } from './plugins/index.js';
+
+const packageDotJSON = require(path.resolve(process.cwd(), './package.json'));
+
+export function makeBaseNPMConfig(options = {}) {
+  const { entrypoints = ['src/index.ts'] } = options;
+
+  const nodeResolvePlugin = makeNodeResolvePlugin();
+  const sucrasePlugin = makeSucrasePlugin();
+
+  return {
+    input: entrypoints,
+
+    output: {
+      sourcemap: true,
+
+      // output individual files rather than one big bundle
+      preserveModules: true,
+
+      // any wrappers or helper functions generated by rollup can use ES6 features
+      generatedCode: 'es2015',
+
+      // don't add `"use strict"` to the top of cjs files
+      strict: false,
+
+      // do TS-3.8-style exports
+      //     exports.dogs = are.great
+      // rather than TS-3.9-style exports
+      //     Object.defineProperty(exports, 'dogs', {
+      //       enumerable: true,
+      //       get: () => are.great,
+      //     });
+      externalLiveBindings: false,
+    },
+
+    plugins: [nodeResolvePlugin, sucrasePlugin],
+
+    // don't include imported modules from outside the package in the final output
+    external: [
+      ...builtinModules,
+      ...Object.keys(packageDotJSON.dependencies || {}),
+      ...Object.keys(packageDotJSON.devDependencies || {}),
+      ...Object.keys(packageDotJSON.peerDependencies || {}),
+    ],
+
+    // TODO `'smallest'` will get rid of `isDebugBuild()` by evaluating it and inlining the result and then treeshaking
+    // from there. The current setting (false) prevents this, in case we want to leave it there for users to use in
+    // their own bundling. That said, we don't yet know for sure that that works, so come back to this.
+    // treeshake: 'smallest',
+    treeshake: false,
+  };
+}
+
+export function makeNPMConfigVariants(baseConfig) {
+  const variantSpecificConfigs = [
+    { output: { format: 'cjs', dir: 'build/cjs' } },
+    { output: { format: 'esm', dir: 'build/esm' } },
+  ];
+
+  return variantSpecificConfigs.map(variant => deepMerge(baseConfig, variant));
+}

rollup/plugins/index.js

@@ -1 +1,2 @@
 export * from './bundlePlugins';
+export * from './npmPlugins';

rollup/plugins/npmPlugins.js

@@ -0,0 +1,16 @@
+/**
+ * Sucrase plugin docs: https://github.com/rollup/plugins/tree/master/packages/sucrase
+ */
+
+import sucrase from '@rollup/plugin-sucrase';
+
+/**
+ * Create a plugin to transpile TS syntax using `sucrase`.
+ *
+ * @returns An instance of the `@rollup/plugin-sucrase` plugin
+ */
+export function makeSucrasePlugin() {
+  return sucrase({
+    transforms: ['typescript', 'jsx'],
+  });
+}