用js判断一个字符串中某个字符出现的次数

<script>
	var nowpic=0
	var patt1=new RegExp("t","g");
	do
	{
		result=patt1.exec("The best things in life are free");
		nowpic++
	}
	while (result!=null) 
	document.write(nowpic-1);
</script>