input_value_to_comma_separated_value.js

function format(input) {
    // input.value = (input.value).toLocaleString('en-US');
    var nStr = input.value + "";
    nStr = nStr.replace(/\,/g, "");
    x = nStr.split(".");
    x1 = x[0];
    x2 = x.length > 1 ? "." + x[1] : "";
    var rgx = /(\d+)(\d{3})/;
    while (rgx.test(x1)) {
        x1 = x1.replace(rgx, "$1" + "," + "$2");
    }
    input.value = x1 + x2;
}