Javascript - format a number with commas and decimals

function formatNumber(value, decimalPlaces) {
        if(isNaN(value) || ""==value) {
            value = 0;
        }
        value = parseFloat(value).toFixed(decimalPlaces);
        return parseInt(value).toLocaleString().split(".")[0] + "." + value.split(".")[1];      
    }

Eg:  7389948 --> 7,389,948.00

If we want the reverse to happen ( 7,389,948.00 --> 7389948)
var a = receivedField.value.replace(/,/g, "");