From b93e2637a3f4f391f2b28ba856a4a464611ed7df Mon Sep 17 00:00:00 2001
From: Daijiro Wachi <daijiro.wachi@gmail.com>
Date: Sun, 28 Jun 2026 02:21:32 +0900
Subject: [PATCH] fix(console): console.assert() logs on failure, not on
 success
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console.assert()'s condition was inverted: `if (!condition) return`
made it stay silent when the assertion failed and print "Assertion
failed" when it passed — the opposite of the cited Console spec, whose
step 1 is "If condition is true, return."

Also use JS::ToBoolean() instead of Value::toBoolean(): the latter
asserts the argument is already a boolean and crashes a debug build (UB
in release) on a non-boolean condition such as console.assert(0). The
spec coerces condition to a boolean.

Add an e2e test asserting the serve stdout for truthy/falsy and
boolean/non-boolean conditions.

Signed-off-by: Daijiro Wachi <daijiro.wachi@gmail.com>
---
 builtins/web/console.cpp                         |  4 ++--
 tests/e2e/console-assert/console-assert.js       | 16 ++++++++++++++++
 tests/e2e/console-assert/expect_serve_stdout.txt |  7 +++++++
 tests/tests.cmake                                |  1 +
 4 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 tests/e2e/console-assert/console-assert.js
 create mode 100644 tests/e2e/console-assert/expect_serve_stdout.txt

diff --git a/builtins/web/console.cpp b/builtins/web/console.cpp
index a2551d52..a5a18f5e 100644
--- a/builtins/web/console.cpp
+++ b/builtins/web/console.cpp
@@ -471,9 +471,9 @@ static bool console_out(JSContext *cx, unsigned argc, JS::Value *vp) {
 static bool assert_(JSContext *cx, unsigned argc, JS::Value *vp) {
   JS::CallArgs args = CallArgsFromVp(argc, vp);
   args.rval().setUndefined();
-  auto condition = args.get(0).toBoolean();
+  auto condition = JS::ToBoolean(args.get(0));
   // 1. If condition is true, return.
-  if (!condition) {
+  if (condition) {
     return true;
   }
 
diff --git a/tests/e2e/console-assert/console-assert.js b/tests/e2e/console-assert/console-assert.js
new file mode 100644
index 00000000..094fe8fc
--- /dev/null
+++ b/tests/e2e/console-assert/console-assert.js
@@ -0,0 +1,16 @@
+// https://console.spec.whatwg.org/#assert
+// console.assert must stay SILENT when the condition is truthy and only log
+// "Assertion failed" when the condition is falsy. The condition is coerced to
+// a boolean, so non-boolean values must be accepted too.
+addEventListener("fetch", (event) => {
+  console.log("a");
+  console.assert(true); // truthy -> silent
+  console.log("b");
+  console.assert(false); // falsy -> logs "Assertion failed"
+  console.log("c");
+  console.assert(1); // truthy non-boolean -> silent
+  console.log("d");
+  console.assert(0); // falsy non-boolean -> logs "Assertion failed"
+  console.log("e");
+  event.respondWith(new Response("ok"));
+});
diff --git a/tests/e2e/console-assert/expect_serve_stdout.txt b/tests/e2e/console-assert/expect_serve_stdout.txt
new file mode 100644
index 00000000..05f2695c
--- /dev/null
+++ b/tests/e2e/console-assert/expect_serve_stdout.txt
@@ -0,0 +1,7 @@
+stdout [0] :: Log: a
+stdout [0] :: Log: b
+stdout [0] :: Error: Assertion failed
+stdout [0] :: Log: c
+stdout [0] :: Log: d
+stdout [0] :: Error: Assertion failed
+stdout [0] :: Log: e
diff --git a/tests/tests.cmake b/tests/tests.cmake
index 7b7840f3..7045a364 100644
--- a/tests/tests.cmake
+++ b/tests/tests.cmake
@@ -46,6 +46,7 @@ function(integration_tests)
 endfunction()
 
 test_e2e(blob)
+test_e2e(console-assert)
 test_e2e(eventloop-stall)
 test_e2e(headers)
 test_e2e(runtime-err)