LayoutTests/js/dom/exception-thrown-from-equal.html

<p>This page tests whether primitive conversions during equality tests properly
throw exceptions. If the test passes, you'll see a series of PASS messages below.
</p>
<hr>
<pre id="console"></pre>

<script>
function log(s)
{
    document.getElementById("console").appendChild(document.createTextNode(s + "\n"));
}

function shouldThrow(expression, exception, didCorrectlyThrow)
{
    if (didCorrectlyThrow)
        log("PASS: " + expression + " should throw a " + exception + ", and did.");
    else
        log("FAIL: " + expression + " should throw a " + exception + ", but didn't.");
}

if (window.testRunner)
    testRunner.dumpAsText();

var o = {
    valueOf: function() {
        return { }; // should throw, because this is not a primitive value
    },
    
    toString: function() {
        return { }; // should throw, because this is not a primitive value
    }
};

shouldThrow("o == 'a'", "type error", (function() { try { o == 'a'; return false; } catch(e) { return e instanceof TypeError; } })());
shouldThrow("o != 'a'", "type error", (function() { try { o != 'a'; return false; } catch(e) { return e instanceof TypeError; } })());
shouldThrow("o == 0", "type error", (function() { try { o == 'a'; return false; } catch(e) { return e instanceof TypeError; } })());
shouldThrow("o != 0", "type error", (function() { try { o != 'a'; return false; } catch(e) { return e instanceof TypeError; } })());
</script>