javascript把数字每隔三位加逗号分开

function addCommas(nStr)
{
	nStr += '';
	x = nStr.split('.');
	x1 = x[0];
	x2 = x.length > 1 ? '.' + x[1] : '';
	var rgx = /(\d+)(\d{3})/;
	while (rgx.test(x1)) {
		x1 = x1.replace(rgx, '$1' + ',' + '$2');
	}
	return x1 + x2;

}

addCommas(1000)
// 1,000

addCommas(1231.897243)
// 1,231.897243

addCommas('9999999.00')
// 9,999,999.00

addCommas(-500000.99)
// -500,000.99