I was curious too, so here's a jsPerf: http://jsperf.com/check-for-undefined-argument http://jsperf.com/check-for-undefined-argument On Chrome 35, looks like

I was curious too, so here's a jsPerf: http://jsperf.com/check-for-undefined-argument http://jsperf.com/check-for-undefined-argument On Chrome 35, looks like comparing to void 0 is a bit faster. Would love some more samples though.