js實現四舍六入 奇進偶舍

function PointFloat(src, pos) {

return Math.round(src * Math.pow(10, pos)) / Math.pow(10, pos);
}

 

//保留小數位數 四舍六入奇進偶舍

function fomatFloat(src, pos) {

var numArray, resultSymbol = "";
if (src < 0) {
resultSymbol = "-";
}
if (pos == "") {
pos = new Number(0);
}
src = src.toString().replace("-", "");
if (src.indexOf('.') > 0) {
numArray = src.split('.');
if (numArray[1].length > pos) {
var endStr, isCarry=false;
if (numArray[1].length > parseFloat(pos) + 1) {
endStr = numArray[1].substring(parseFloat(pos) + 1);
for (var i = 0; i < endStr.length; i++) {
if (endStr[i] > 0) {
isCarry = true;
break;
}
}
}
numArray[1] = numArray[1].substring(0, pos + 1);
var endChar = numArray[1][pos];
var newpoint = new Number("0." + numArray[1].substring(0, pos));
if (endChar >= 5 && pos >= 0) {
if (endChar > 5) {
if (pos == 0) {
numArray[1] = 1;
}
else {
numArray[1] = parseFloat(newpoint) + parseFloat(Math.pow(0.1, pos));
}
}
else if (endChar == 5) {
//5后面有有效數字，直接向前進一位
if (isCarry) {
numArray[1] = parseFloat(newpoint) + parseFloat(Math.pow(0.1, pos));
return PointFloat(resultSymbol + eval(numArray.join("+")), pos);
}
if (pos == 0) {
if (numArray[0] % 2 != 0) {
numArray[1] = 1;
} else {
numArray[1] = 0;
}
return PointFloat(resultSymbol + eval(numArray.join("+")), pos);
}
var preChar = numArray[1][pos - 1];
if (preChar % 2 == 0) {
numArray[1] = newpoint;
}
else {
numArray[1] = parseFloat(newpoint) + parseFloat(Math.pow(0.1, pos));
}
}
return PointFloat(resultSymbol + eval(numArray.join("+")), pos);
}
else {
numArray[1] = newpoint;
return PointFloat(resultSymbol + eval(numArray.join("+")), pos);
}
}
return src;

} else {
return resultSymbol + src;
}
return src;
}