js 四舍五入 保留自定义位数小数 的 函数

function   round(v,e)
{
var   t=1;
for(;e>0;t*=10,e--);
for(;e<0;t/=10,e++);
return   Math.round(v*t)/t;
}

function FormatNumber(srcStr,nAfterDot){
var srcStr,nAfterDot;
var resultStr,nTen;
srcStr = ""+srcStr+"";
strLen = srcStr.length;
dotPos = srcStr.indexOf(".",0);
if (dotPos == -1){
resultStr = srcStr+".";
for (i=0;i<nAfterDot;i++){
resultStr = resultStr+"0";
}
}
else{
if ((strLen - dotPos - 1) >= nAfterDot){
nAfter = dotPos + nAfterDot + 1;
nTen =1;
for(j=0;j<nAfterDot;j++){
nTen = nTen*10;
}
resultStr = Math.round(parseFloat(srcStr)*nTen)/nTen;
}
else{
resultStr = srcStr;
for (i=0;i<(nAfterDot - strLen + dotPos + 1);i++){
resultStr = resultStr+"0";
}

}
}

return resultStr;

}