v8/test/mjsunit/regress/regress-2438.js

// Copyright 2012 the V8 project authors. All rights reserved.
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function testSideEffects(subject, re) {
  var counter = 0;
  var expected_counter = 0;
  const accesses_lastindex = (re.global || re.sticky);
  var side_effect_object = { valueOf: function() { return counter++; } };
  re.lastIndex = side_effect_object;
  re.exec(subject);

  if (accesses_lastindex) expected_counter++;
  assertEquals(expected_counter, counter);

  re.lastIndex = side_effect_object;
  re.test(subject);

  if (accesses_lastindex) expected_counter++;
  assertEquals(expected_counter, counter);
}

testSideEffects("zzzz", /a/);
testSideEffects("zzzz", /a/g);
testSideEffects("xaxa", /a/);
testSideEffects("xaxa", /a/g);