# Format a number 2 : Number Data Type « Language Basics « JavaScript DHTML

Format a number 2

```

<!--
Example File From "JavaScript and DHTML Cookbook"
-->
function formatCommas(numString) {
var re = /(-?\d+)(\d{3})/;
while (re.test(numString)) {
numString = numString.replace(re, "\$1,\$2");
}
return numString;
}

function formatNumber (num, decplaces) {
// convert in case it arrives as a string value
num = parseFloat(num);
// make sure it passes conversion
if (!isNaN(num)) {
// multiply value by 10 to the decplaces power;
// round the result to the nearest integer;
// convert the result to a string
var str = "" + Math.round (eval(num) * Math.pow(10,decplaces));
// exponent means value is too big or small for this routine
if (str.indexOf("e") != -1) {
return "Out of Range";
}
// if needed for small values, pad zeros
// to the left of the number
while (str.length <= decplaces) {
str = "0" + str;
}
// calculate decimal point position
var decpoint = str.length - decplaces;
// assemble final result from: (a) the string up to the position of
// the decimal point; (b) the decimal point; and (c) the balance
// of the string. Return finished product.
return formatCommas(str.substring(0,decpoint)) + "." + str.substring(decpoint,str.length);

} else {
return "NaN";
}
}

```

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