v8/test/mjsunit/global-const-var-conflicts.js

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// Check that dynamically introducing conflicting consts/vars
// is silently ignored (and does not lead to exceptions).

var caught = 0;

eval("const a");
try { eval("var a"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
assertTrue(typeof a == 'undefined');
try { eval("var a = 1"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
assertTrue(typeof a == 'undefined');

eval("const b = 0");
try { eval("var b"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
assertEquals(0, b);
try { eval("var b = 1"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
assertEquals(0, b);
assertEquals(0, caught);

eval("var c");
try { eval("const c"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
assertTrue(typeof c == 'undefined');
assertEquals(1, caught);
try { eval("const c = 1"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
assertEquals(undefined, c);
assertEquals(2, caught);

eval("var d = 0");
try { eval("const d"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
assertEquals(0, d);
assertEquals(3, caught);
try { eval("const d = 1"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
assertEquals(0, d);
assertEquals(4, caught);