From c1fb0c2f938b2ed586089ccc08657beef5673258 Mon Sep 17 00:00:00 2001
From: Kevin Gibbons <bakkot@gmail.com>
Date: Sun, 7 Dec 2025 18:59:22 -0800
Subject: [PATCH] add polyfill / test262 runner

---
 polyfill.js     | 57 +++++++++++++++++++++++++++++++++++++++++++++++++
 run-test262.mjs | 38 +++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+)
 create mode 100644 polyfill.js
 create mode 100644 run-test262.mjs

diff --git a/polyfill.js b/polyfill.js
new file mode 100644
index 0000000..8047ec2
--- /dev/null
+++ b/polyfill.js
@@ -0,0 +1,57 @@
+'use strict';
+
+// this polyfill is spec-accurate, but not something you should actually use
+
+let join = {
+  join(separator) {
+    if (!this || typeof this !== 'object' && typeof this !== 'function') {
+      throw new TypeError('expected receiver to be an object');
+    }
+    let sep;
+    if (separator === undefined) {
+      sep = ',';
+    } else {
+      try {
+        sep = `${separator}`;
+      } catch (e) {
+        try {
+          this.return();
+        } catch { /* ignored */ }
+        throw e;
+      }
+    }
+    let next = this.next;
+    let R = '';
+    let first = true;
+    while (true) {
+      let { done, value } = next.call(this);
+      if (done) {
+        return R;
+      }
+      if (first) {
+        first = false;
+      } else {
+        R = R + sep;
+      }
+      if (value !== undefined && value !== null) {
+        let S;
+        try {
+          S = `${value}`;
+        } catch (e) {
+          try {
+            this.return();
+          } catch { /* ignored */ }
+          throw e;
+        }
+        R = R + S;
+      }
+    }
+  }
+}.join;
+
+Object.defineProperty(Iterator.prototype, 'join', {
+  configurable: true,
+  writable: true,
+  enumerable: false,
+  value: join,
+});
diff --git a/run-test262.mjs b/run-test262.mjs
new file mode 100644
index 0000000..2c28398
--- /dev/null
+++ b/run-test262.mjs
@@ -0,0 +1,38 @@
+// assumes test262 is checked out in ../test262
+
+import fs from 'node:fs';
+import vm from 'node:vm';
+
+let testDir = '../test262/test/built-ins/Iterator';
+let files = fs.readdirSync(testDir, { recursive: true });
+
+let harness =
+  fs.readFileSync('polyfill.js', 'utf8') +
+[
+  '../test262/harness/assert.js',
+  '../test262/harness/compareArray.js',
+  '../test262/harness/isConstructor.js',
+  '../test262/harness/iteratorZipUtils.js',
+  '../test262/harness/propertyHelper.js',
+  '../test262/harness/proxyTrapsHelper.js',
+  '../test262/harness/testTypedArray.js',
+  '../test262/harness/wellKnownIntrinsicObjects.js',
+].map(x => fs.readFileSync(x, 'utf8')).join('\n') + `
+var $DETACHBUFFER = buff => buff.transfer();
+class Test262Error extends Error {}
+`;
+
+for (let file of files) {
+  if (!file.endsWith('.js')) continue;
+  let basic = fs.readFileSync(testDir + '/' + file, 'utf8');
+  if (!basic.includes('Iterator.prototype.join')) continue;
+  console.log(testDir + '/' + file);
+  let contents = harness + '\n(function(){ ' + basic + '})()';
+  try {
+    vm.runInContext(contents, vm.createContext({ console }));
+  } catch (e) {
+    fs.writeFileSync('evaluated-test262.js', contents, 'utf8');
+    console.log('evaluated-test262.js')
+    throw e;
+  }
+}