js取小數點后兩位四種方法

function getnum()
{
var num = 22.123456;
var result = num.substring(0,s.indexOf(".")+3);
alert(result);
}

function getnum()
{
var num = 22.123456;
var aNew;
var re = /([0-9]+\.[0-9]{2})[0-9]*/;
aNew = num.replace(re,"$1");
alert(aNew);
}

function getnum()
{
var num=22.123456;
alert( Math.round(num*100)/100);
}

alert(num.toFixed(2));