Reveiw

.gitignore

@@ -10,5 +10,8 @@ node_modules
 # WebPack build output
 dist
 
+# Generated wasm-bindgen bundler + wasm2js output for the React Native build
+pkg-rn
+
 # Python virtual environment
 .venv

README.md

@@ -80,6 +80,13 @@ console.log(result.text); // "Hi beautiful world"
 
 See the [example website source](examples/website/src/index.ts) for a more complex example, or the [advanced examples document](docs/advanced-ts.md).
 
+#### React Native (Hermes)
+
+React Native's default engine, Hermes, does not expose a runtime `WebAssembly`
+global, so the WebAssembly build cannot run there. For React Native, the package
+ships a [`wasm2js`](https://github.com/WebAssembly/binaryen) (pure-JavaScript)
+build via its `react-native` entry point.
+
 ### Python
 
 Install via uv or pip:

reconcile-js/package-lock.json

@@ -10,6 +10,7 @@
       "license": "MIT",
       "devDependencies": {
         "@types/jest": "^30.0.0",
+        "binaryen": "^123.0.0",
         "jest": "^30.3.0",
         "prettier": "^3.8.1",
         "reconcile-text": "file:../pkg",
@@ -65,6 +66,7 @@
       "version": "7.28.0",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "@ampproject/remapping": "^2.2.0",
         "@babel/code-frame": "^7.27.1",
@@ -1656,6 +1658,7 @@
       "integrity": "sha512-UVJyE9MttOsBQIDKw1skb9nAwQuR5wuGD3+82K6JgJlm/Y+KI92oNsMNGZCYdDsVtRHSak0pcV5Dno5+4jh9sw==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "bin": {
         "acorn": "bin/acorn"
       },
@@ -1682,6 +1685,7 @@
       "integrity": "sha512-PlXPeEWMXMZ7sPYOHqmDyCJzcfNrUr3fGNKtezX14ykXOEIvyK81d+qydx89KY5O71FKMPaQ2vBfBFI5NHR63A==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "fast-deep-equal": "^3.1.3",
         "fast-uri": "^3.0.1",
@@ -1908,6 +1912,24 @@
         "node": ">=6.0.0"
       }
     },
+    "node_modules/binaryen": {
+      "version": "123.0.0",
+      "resolved": "https://registry.npmjs.org/binaryen/-/binaryen-123.0.0.tgz",
+      "integrity": "sha512-/hls/a309aZCc0itqP6uhoR+5DsKSlJVfB8Opd2BY9Ndghs84IScTunlyidyF4r2Xe3lQttnfBNIDjaNpj6mTw==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "wasm-as": "bin/wasm-as",
+        "wasm-ctor-eval": "bin/wasm-ctor-eval",
+        "wasm-dis": "bin/wasm-dis",
+        "wasm-merge": "bin/wasm-merge",
+        "wasm-metadce": "bin/wasm-metadce",
+        "wasm-opt": "bin/wasm-opt",
+        "wasm-reduce": "bin/wasm-reduce",
+        "wasm-shell": "bin/wasm-shell",
+        "wasm2js": "bin/wasm2js"
+      }
+    },
     "node_modules/brace-expansion": {
       "version": "1.1.12",
       "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-1.1.12.tgz",
@@ -1950,6 +1972,7 @@
         }
       ],
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "baseline-browser-mapping": "^2.9.0",
         "caniuse-lite": "^1.0.30001759",
@@ -3053,6 +3076,7 @@
       "integrity": "sha512-AkXIIFcaazymvey2i/+F94XRnM6TsVLZDhBMLsd1Sf/W0wzsvvpjeyUrCZD6HGG4SDYPgDJDBKeiJTBb10WzMg==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "@jest/core": "30.3.0",
         "@jest/types": "30.3.0",
@@ -4936,6 +4960,7 @@
       "integrity": "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==",
       "dev": true,
       "license": "Apache-2.0",
+      "peer": true,
       "bin": {
         "tsc": "bin/tsc",
         "tsserver": "bin/tsserver"
@@ -5072,6 +5097,7 @@
       "integrity": "sha512-jTywjboN9aHxFlToqb0K0Zs9SbBoW4zRUlGzI2tYNxVYcEi/IPpn+Xi4ye5jTLvX2YeLuic/IvxNot+Q1jMoOw==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "@types/eslint-scope": "^3.7.7",
         "@types/estree": "^1.0.8",
@@ -5119,6 +5145,7 @@
       "version": "6.0.1",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "@discoveryjs/json-ext": "^0.6.1",
         "@webpack-cli/configtest": "^3.0.1",

reconcile-js/package.json

@@ -4,6 +4,7 @@
   "description": "Intelligent 3-way text merging with automated conflict resolution",
   "main": "dist/reconcile.node.js",
   "browser": "dist/reconcile.web.js",
+  "react-native": "dist/reconcile.rn.js",
   "keywords": [
     "text editing",
     "sync",
@@ -31,12 +32,13 @@
     "dist/**/*"
   ],
   "scripts": {
-    "build": "webpack --mode production",
+    "build": "node scripts/build-rn.mjs && webpack --mode production",
     "format": "prettier --write \"./**/*.(ts|scss|json|html)\"",
     "test": "NODE_OPTIONS=\"$NODE_OPTIONS --experimental-vm-modules\" jest"
   },
   "devDependencies": {
     "@types/jest": "^30.0.0",
+    "binaryen": "^123.0.0",
     "jest": "^30.3.0",
     "prettier": "^3.8.1",
     "reconcile-text": "file:../pkg",

reconcile-js/src/index.rn.test.ts

@@ -0,0 +1,95 @@
+import { reconcile, reconcileWithHistory, diff, undiff } from './index.rn';
+import { installWasmLeakDetector, checkForWasmLeaks } from './wasm-leak-detector';
+import * as fs from 'fs';
+import * as path from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+installWasmLeakDetector();
+
+afterEach(() => {
+  const leaks = checkForWasmLeaks();
+  if (leaks.length > 0) {
+    throw new Error(
+      `WASM memory leak: ${leaks.length} object(s) not freed:\n  ${leaks.join('\n  ')}`
+    );
+  }
+});
+
+describe('reconcile (wasm2js / React Native build)', () => {
+  it('call reconcile without cursors', () => {
+    expect(reconcile('Hello', 'Hello world', 'Hi world').text).toEqual('Hi world');
+  });
+
+  it('call reconcile with cursors', () => {
+    const result = reconcile(
+      'Hello',
+      {
+        text: 'Hello world',
+        cursors: [
+          {
+            id: 3,
+            position: 2,
+          },
+        ],
+      },
+      {
+        text: 'Hi world',
+        cursors: [
+          {
+            id: 4,
+            position: 0,
+          },
+          { id: 5, position: 3 },
+        ],
+      }
+    );
+
+    expect(result.text).toEqual('Hi world');
+    expect(result.cursors).toEqual([
+      { id: 3, position: 0 },
+      { id: 4, position: 0 },
+      { id: 5, position: 3 },
+    ]);
+  });
+
+  it('call reconcileWithHistory', () => {
+    const result = reconcileWithHistory('Hello', 'Hello world', 'Hi world');
+
+    expect(result.text).toEqual('Hi world');
+    expect(result.history.length).toBeGreaterThan(0);
+  });
+});
+
+describe('test_diff_and_undiff_are_inverse (wasm2js / React Native build)', () => {
+  const resourcesPath = path.join(__dirname, '../../tests/resources');
+
+  const readFileSlice = (fileName: string, start: number, end: number): string => {
+    const filePath = path.join(resourcesPath, fileName);
+    const content = fs.readFileSync(filePath, 'utf-8');
+    const chars = Array.from(content); // Handle unicode properly
+    return chars.slice(start, Math.min(end, chars.length)).join('');
+  };
+
+  const files = ['pride_and_prejudice.txt', 'room_with_a_view.txt', 'blns.txt'];
+
+  const ranges = [{ start: 0, end: 50000 }];
+
+  files.forEach((file1) => {
+    files.forEach((file2) => {
+      ranges.forEach((range1) => {
+        ranges.forEach((range2) => {
+          it(`should diff & undiff ${file1}[${range1.start}..${range1.end}], ${file2}[${range2.start}..${range2.end}] without panic`, () => {
+            const content1 = readFileSlice(file1, range1.start, range1.end);
+            const content2 = readFileSlice(file2, range2.start, range2.end);
+
+            const changes = diff(content1, content2);
+            const actual = undiff(content1, changes);
+            expect(actual).toEqual(content2);
+          });
+        });
+      });
+    });
+  });
+});

reconcile-js/src/index.rn.ts

@@ -0,0 +1,47 @@
+// React Native entrypoint (resolved via the `react-native` package field).
+//
+// Hermes — the default React Native engine since RN 0.84 / Expo SDK 56 — does
+// not expose a runtime `WebAssembly` global, so the normal `new
+// WebAssembly.Module(...)` path used by `index.ts` throws
+// `ReferenceError: Property 'WebAssembly' doesn't exist`.
+//
+// Instead we link a wasm2js translation of the module: pure JavaScript that
+// needs no `WebAssembly` global and is instantiated synchronously at import
+// time. The public API and its synchronous signatures are unchanged, so
+// callers need no modification. The `pkg-rn` directory is generated by
+// `scripts/build-rn.mjs`.
+
+import {
+  CursorPosition as wasmCursorPosition,
+  TextWithCursors as wasmTextWithCursors,
+  reconcile as wasmReconcile,
+  reconcileWithHistory as wasmReconcileWithHistory,
+  diff as wasmDiff,
+  undiff as wasmUndiff,
+} from '../pkg-rn/reconcile_text.js';
+
+import { makeReconcileApi, type WasmBackend } from './core';
+
+const backend: WasmBackend = {
+  CursorPosition: wasmCursorPosition,
+  TextWithCursors: wasmTextWithCursors,
+  reconcile: wasmReconcile,
+  reconcileWithHistory: wasmReconcileWithHistory,
+  diff: wasmDiff,
+  undiff: wasmUndiff,
+  // The wasm2js module initialises itself at import time, so this is a no-op.
+  ensureReady() {},
+};
+
+export const { reconcile, diff, undiff, reconcileWithHistory } =
+  makeReconcileApi(backend);
+
+export type {
+  BuiltinTokenizer,
+  History,
+  CursorPosition,
+  TextWithCursors,
+  TextWithOptionalCursors,
+  TextWithCursorsAndHistory,
+  SpanWithHistory,
+} from './core';

reconcile-js/src/index.ts

@@ -1,8 +1,7 @@
 import {
   CursorPosition as wasmCursorPosition,
-  reconcile as wasmReconcile,
   TextWithCursors as wasmTextWithCursors,
-  SpanWithHistory as wasmSpanWithHistory,
+  reconcile as wasmReconcile,
   reconcileWithHistory as wasmReconcileWithHistory,
   diff as wasmDiff,
   undiff as wasmUndiff,
@@ -11,341 +10,40 @@ import {
 
 import wasmBytes from 'reconcile-text/reconcile_text_bg.wasm';
 
-// Define the enum values as const arrays to avoid duplication
+import { makeReconcileApi, type WasmBackend } from './core';
-const BUILTIN_TOKENIZERS = ['Character', 'Line', 'Markdown', 'Word'] as const;
-const HISTORY_VALUES = [
-  'Unchanged',
-  'AddedFromLeft',
-  'AddedFromRight',
-  'RemovedFromLeft',
-  'RemovedFromRight',
-] as const;
-
-/**
- * Tokenisation strategies for text merging.
- *
- * These correspond to the built-in tokenizers available in the underlying WASM module.
- */
-export type BuiltinTokenizer = (typeof BUILTIN_TOKENIZERS)[number];
-
-/**
- * History classification for text spans in merge results.
- *
- * Indicates the origin of each text span in the merged document.
- */
-export type History = (typeof HISTORY_VALUES)[number];
-
-/**
- * Represents a text document with associated cursor positions.
- *
- * This interface is used both as input to reconcile functions (to specify where
- * cursors are positioned in the original documents) and as output (with cursors
- * automatically repositioned after merging).
- */
-export interface TextWithCursors {
-  /** The document's entire content as a string */
-  text: string;
-
-  /**
-   * Array of cursor positions within the text. Can be empty if there are no cursors to track.
-   * Each cursor has a unique ID and position.
-   */
-  cursors: CursorPosition[];
-}
-
-/**
- * Like `TextWithCursors`, but cursors may be null or undefined (treated as empty).
- * Used as input where cursor tracking is optional.
- */
-export interface TextWithOptionalCursors {
-  /** The document's entire content as a string */
-  text: string;
-
-  /**
-   * Array of cursor positions within the text. Can be null, undefined, or empty
-   * if there are no cursors to track. Each cursor has a unique ID and position.
-   */
-  cursors: null | undefined | CursorPosition[];
-}
-
-/**
- * Represents a cursor position within a text document.
- *
- * Cursors are automatically repositioned during text merging to maintain their
- * relative positions as text is inserted, deleted, or modified around them.
- */
-export interface CursorPosition {
-  /** Unique identifier for the cursor (can be any number, must be unique within the document) */
-  id: number;
-
-  /** Character position in the text, 0-based index from the beginning of the document */
-  position: number;
-}
-
-/**
- * Represents a merged text document with cursor positions and detailed change history.
- *
- * This is the return type of `reconcileWithHistory()` and provides complete information
- * about how the merge was performed, including which parts of the final text came from
- * which source documents.
- */
-export interface TextWithCursorsAndHistory {
-  /** The merged document's entire content */
-  text: string;
-
-  /**
-   * Array of cursor positions within the merged text. Can be empty if there are no cursors to track.
-   * All cursors are automatically repositioned from the left and right documents.
-   */
-  cursors: CursorPosition[];
-
-  /**
-   * Detailed provenance information showing the origin of each text span in the result.
-   * Each span indicates whether it was unchanged, added from left, added from right, etc.
-   */
-  history: SpanWithHistory[];
-}
-
-/**
- * Represents a span of text in the merged result with its change history.
- *
- * This shows exactly which source document contributed each piece of text to the
- * final merged result. Useful for understanding merge decisions and creating
- * visualisations of how documents were combined.
- */
-export interface SpanWithHistory {
-  /** The text content of this span */
-  text: string;
-
-  /** The origin of this text span in the merge result */
-  history: History;
-}
-
-const UNSUPPORTED_TOKENIZER_ERROR = `Unsupported tokenizer, only ${BUILTIN_TOKENIZERS.join(
-  ', '
-)} are supported`;
 
 let isInitialised = false;
 
-/**
+const backend: WasmBackend = {
- * Merges three versions of text using intelligent conflict resolution.
+  CursorPosition: wasmCursorPosition,
- *
+  TextWithCursors: wasmTextWithCursors,
- * This is the primary function for 3-way text merging. Unlike traditional merge tools
+  reconcile: wasmReconcile,
- * that produce conflict markers, this function automatically resolves conflicts by
+  reconcileWithHistory: wasmReconcileWithHistory,
- * applying both sets of changes where possible.
+  diff: wasmDiff,
- *
+  undiff: wasmUndiff,
- * @param original - The original/base version of the text that both sides diverged from
+  ensureReady() {
- * @param left - The left version of the text (either string or TextWithCursors with cursor positions)
+    if (isInitialised) {
- * @param right - The right version of the text (either string or TextWithCursors with cursor positions)
+      return;
- * @param tokenizer - The tokenisation strategy: "Word" (default, recommended for prose),
+    }
- *                    "Character" (fine-grained), or "Line" (similar to git merge)
- * @returns The reconciled text with automatically repositioned cursor positions
- *
- * @example
- * ```typescript
- * const original = "Hello world";
- * const left = "Hello beautiful world";    // Added "beautiful"
- * const right = "Hi world";                // Changed "Hello" to "Hi"
- *
- * const result = reconcile(original, left, right);
- * console.log(result.text); // "Hi beautiful world"
- * ```
- */
-export function reconcile(
-  original: string,
-  left: string | TextWithOptionalCursors,
-  right: string | TextWithOptionalCursors,
-  tokenizer: BuiltinTokenizer = 'Word'
-): TextWithCursors {
-  init();
 
-  if (!BUILTIN_TOKENIZERS.includes(tokenizer)) {
+    const wasmBinary = Uint8Array.from(atob(wasmBytes as unknown as string), (c) =>
-    throw new Error(UNSUPPORTED_TOKENIZER_ERROR);
+      c.charCodeAt(0)
-  }
+    );
+    initSync({ module: wasmBinary });
 
-  const leftCursor = toWasmTextWithCursors(left);
+    isInitialised = true;
-  const rightCursor = toWasmTextWithCursors(right);
+  },
+};
 
-  const result = wasmReconcile(original, leftCursor, rightCursor, tokenizer);
+export const { reconcile, diff, undiff, reconcileWithHistory } =
+  makeReconcileApi(backend);
 
-  leftCursor.free();
+export type {
-  rightCursor.free();
+  BuiltinTokenizer,
-
+  History,
-  const jsResult = toTextWithCursors(result);
+  CursorPosition,
-  result.free();
+  TextWithCursors,
-
+  TextWithOptionalCursors,
-  return jsResult;
+  TextWithCursorsAndHistory,
-}
+  SpanWithHistory,
-
+} from './core';
-/**
- * Generates a compact diff representation between an original and changed text.
- *
- * These can be parsed and unpacked using the `undiff` function or the Rust crate's EditedText::from_diff.
- * Cursor positions are omitted from the diff result.
- *
- * This function computes the differences between two versions of text and returns
- * a compact representation of those changes.
- *
- * @param original - The original/base version of the text
- * @param changed - The modified version of the text (either string or TextWithCursors with cursor positions)
- * @param tokenizer - The tokenisation strategy, which is the same as used in `reconcile`.
- * @returns An array of inserts (strings), deletes (negative integers), and retained spans (positive integers).
- */
-export function diff(
-  original: string,
-  changed: string | TextWithOptionalCursors,
-  tokenizer: BuiltinTokenizer = 'Word'
-): Array<number | string> {
-  init();
-
-  if (!BUILTIN_TOKENIZERS.includes(tokenizer)) {
-    throw new Error(UNSUPPORTED_TOKENIZER_ERROR);
-  }
-
-  const changedWasm = toWasmTextWithCursors(changed);
-
-  const result = wasmDiff(original, changedWasm, tokenizer);
-
-  changedWasm.free();
-
-  return result.map((item) => (typeof item === 'bigint' ? Number(item) : item));
-}
-
-/**
- * Applies a compact diff to an original text to reconstruct the changed version.
- *
- * This function takes an original text and a compact diff representation (as produced
- * by the `diff` function) and reconstructs the modified text.
- *
- * @param original - The original/base version of the text
- * @param diff - The compact diff array (inserts as strings, deletes as negative integers, retained spans as positive integers)
- * @param tokenizer - The tokenisation strategy, which is the same as used in `reconcile`.
- * @returns The reconstructed changed text as a string.
- */
-export function undiff(
-  original: string,
-  diff: Array<number | bigint | string>,
-  tokenizer: BuiltinTokenizer = 'Word'
-): string {
-  init();
-
-  if (!BUILTIN_TOKENIZERS.includes(tokenizer)) {
-    throw new Error(UNSUPPORTED_TOKENIZER_ERROR);
-  }
-
-  return wasmUndiff(original, diff, tokenizer);
-}
-
-/**
- * Merges three versions of text and returns detailed provenance information.
- *
- * This function behaves like `reconcile()` but also provides
- * detailed historical information about the origin of each text span in the result.
- * This is valuable for understanding how the merge was performed and which changes
- * came from which source.
- *
- * Note: Computing the history is computationally more expensive than the basic merge.
- *
- * @param original - The original/base version of the text that both sides diverged from
- * @param left - The left version of the text (either string or TextWithCursors with cursor positions)
- * @param right - The right version of the text (either string or TextWithCursors with cursor positions)
- * @param tokenizer - The tokenisation strategy: "Word" (default, recommended for prose),
- *                    "Character" (fine-grained), or "Line" (similar to git merge)
- * @returns The reconciled text with cursor positions and detailed change history
- *
- * @example
- * ```typescript
- * const original = "Hello world";
- * const left = "Hello beautiful world";
- * const right = "Hi world";
- *
- * const result = reconcileWithHistory(original, left, right);
- * console.log(result.text); // "Hi beautiful world"
- * console.log(result.history); // Array of SpanWithHistory objects showing change origins
- * ```
- */
-export function reconcileWithHistory(
-  original: string,
-  left: string | TextWithOptionalCursors,
-  right: string | TextWithOptionalCursors,
-  tokenizer: BuiltinTokenizer = 'Word'
-): TextWithCursorsAndHistory {
-  init();
-
-  if (!BUILTIN_TOKENIZERS.includes(tokenizer)) {
-    throw new Error(UNSUPPORTED_TOKENIZER_ERROR);
-  }
-
-  const leftCursor = toWasmTextWithCursors(left);
-  const rightCursor = toWasmTextWithCursors(right);
-
-  const result = wasmReconcileWithHistory(original, leftCursor, rightCursor, tokenizer);
-
-  leftCursor.free();
-  rightCursor.free();
-
-  const jsResult = toTextWithCursors(result);
-  const history = result.history().map(toSpanWithHistory);
-  result.free();
-
-  return {
-    ...jsResult,
-    history,
-  };
-}
-
-function init() {
-  if (isInitialised) {
-    return;
-  }
-
-  const wasmBinary = Uint8Array.from(atob(wasmBytes as unknown as string), (c) =>
-    c.charCodeAt(0)
-  );
-  initSync({ module: wasmBinary });
-
-  isInitialised = true;
-}
-
-function toWasmTextWithCursors(
-  text: string | TextWithOptionalCursors
-): wasmTextWithCursors {
-  const isInputString = typeof text === 'string';
-  const leftText = isInputString ? text : text.text;
-  const leftCursors = isInputString ? [] : (text.cursors ?? []);
-
-  return new wasmTextWithCursors(leftText, leftCursors.map(toWasmCursorPosition));
-}
-
-function toWasmCursorPosition({ id, position }: CursorPosition): wasmCursorPosition {
-  return new wasmCursorPosition(id, position);
-}
-
-function toTextWithCursors(textWithCursor: wasmTextWithCursors): TextWithCursors {
-  const wasmCursors = textWithCursor.cursors();
-  const cursors = wasmCursors.map(toCursorPosition);
-  for (const cursor of wasmCursors) {
-    cursor.free();
-  }
-
-  return {
-    text: textWithCursor.text(),
-    cursors,
-  };
-}
-
-function toCursorPosition(cursor: wasmCursorPosition): CursorPosition {
-  return {
-    id: cursor.id(),
-    position: cursor.characterIndex(),
-  };
-}
-
-function toSpanWithHistory(span: wasmSpanWithHistory): SpanWithHistory {
-  const result = {
-    text: span.text(),
-    history: span.history(),
-  };
-  span.free();
-  return result;
-}

reconcile-js/webpack.config.js

@@ -2,7 +2,6 @@ const path = require('path');
 const { merge } = require('webpack-merge');
 
 const common = {
-  entry: './src/index.ts',
   optimization: {
     // the consuming project should take care of minification
     minimize: false,
@@ -38,8 +37,10 @@ const common = {
 };
 
 module.exports = [
+  // Web build: real WebAssembly, instantiated synchronously from inlined base64.
   merge(common, {
     target: 'web',
+    entry: './src/index.ts',
     output: {
       path: path.resolve(__dirname, 'dist'),
       filename: 'reconcile.web.js',
@@ -50,12 +51,31 @@ module.exports = [
       globalObject: 'this',
     },
   }),
+
+  // Node build: real WebAssembly.
   merge(common, {
     target: 'node',
+    entry: './src/index.ts',
     output: {
       path: path.resolve(__dirname, 'dist'),
       filename: 'reconcile.node.js',
       libraryTarget: 'commonjs2',
     },
   }),
+
+  // React Native build: wasm2js (pure JS), for Hermes which has no
+  // `WebAssembly` global. Sources come from `pkg-rn/`
+  merge(common, {
+    target: 'web',
+    entry: './src/index.rn.ts',
+    output: {
+      path: path.resolve(__dirname, 'dist'),
+      filename: 'reconcile.rn.js',
+      library: {
+        name: 'reconcile',
+        type: 'umd',
+      },
+      globalObject: 'this',
+    },
+  }),
 ];