cost of trailing comma

q: How many CPU cycles could've been saved if trailing commas were allowed from the start?

JavaScript

var s,start,i,naive,avoid_trailing_comma,times = 1000000;

start = Date.now();
s = '[';
for (i = 0;i<times;i++)
	s+='1,';
s+=']';
naive = Date.now() - start;

start = Date.now();
s = '[';
for (i = 0;i<times;i++){
	if (i)
		s+=',';
	s+='1';
}
s+=']';
avoid_trailing_comma = Date.now() - start;

document.body.innerHTML = 'Trailing comma cost ' + (avoid_trailing_comma - naive) + 'ms per ' + times + ' iterations';