third_party/v8/test/debugger/debug/regress/regress-10319.js

// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

var Debug = debug.Debug;

var frame;

Debug.setListener(function (event, exec_state, event_data, data) {
  if (event == Debug.DebugEvent.Break) {
    frame = exec_state.frame(0);

    // Try changing the value, which hasn't yet been initialized.
    assertEquals(3, frame.evaluate("result = 3").value());
    assertEquals(3, frame.evaluate("result").value());
  }
});

function makeCounter() {
  // If the variable `result` were stack-allocated, it would be 3 at this point
  // due to the debugging activity during function entry. However, for a
  // heap-allocated variable, the debugger evaluated `result = 3` in a temporary
  // scope instead and had no effect on this variable.
  assertEquals(undefined, result);

  var result = 0;

  // Regardless of how `result` is allocated, it should now be initialized.
  assertEquals(0, result);

  // Close over `result` to cause it to be heap-allocated.
  return () => ++result;
}

// Break on entry to a function which includes heap-allocated variables.
%ScheduleBreak();
makeCounter();

// Check the frame state which was collected during the breakpoint.
assertEquals(1, frame.localCount());
assertEquals('result', frame.localName(0));
assertEquals(undefined, frame.localValue(0).value());
assertEquals(3, frame.scopeCount());
assertEquals(debug.ScopeType.Local, frame.scope(0).scopeType());
assertEquals(debug.ScopeType.Script, frame.scope(1).scopeType());
assertEquals(debug.ScopeType.Global, frame.scope(2).scopeType());