Date.UTC() should apply TimeClip operation according to ECMA-262. On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". PASS Date.UTC(275760, 8, 12, 23, 59, 59, 999) is 8639999999999999 PASS Date.UTC(275760, 8, 13) is 8640000000000000 PASS isNaN(Date.UTC(275760, 8, 13, 0, 0, 0, 1)) is true PASS isNaN(Date.UTC(275760, 8, 14)) is true PASS Date.UTC(-271821, 3, 20, 0, 0, 0, 1) is -8639999999999999 PASS Date.UTC(-271821, 3, 20) is -8640000000000000 PASS isNaN(Date.UTC(-271821, 3, 19, 23, 59, 59, 999)) is true PASS isNaN(Date.UTC(-271821, 3, 19)) is true PASS successfullyParsed is true TEST COMPLETE