Removing commas is potentially dangerous because, as others have mentioned in the comments, many locales use a comma to mean something different (like a decimal place).

I don't know where you got your string from, but in some places in the world "2,299.00" = 2.299

The Intl object could have been a nice way to tackle this problem, but somehow they managed to ship the spec with only a Intl.NumberFormat.format() API and no parse counterpart :(

The only way to parse a string with cultural numeric characters in it to a machine recognisable number in any i18n sane way is to use a library that leverages CLDR data to cover off all possible ways of formatting number strings http://cldr.unicode.org/

The two best JS options I've come across for this so far:

• https://github.com/google/closure-library/tree/master/closure/goog/i18n
• https://github.com/globalizejs/globalize

If is about localizing thousands separators, delimiters and decimal separators, go with the following:

// --> numObj.toLocaleString( [locales [, options] ] )
parseInt( number ).toLocaleString();

There are several options you can use (and even locales with fallbacks):

number = 123456.7089;

result  = parseInt( number ).toLocaleString() + "<br>";
result += number.toLocaleString( 'de-DE' ) + "<br>";
result += number.toLocaleString( 'ar-EG' ) + "<br>";
result += number.toLocaleString( 'ja-JP', { 
  style           : 'currency',
  currency        : 'JPY',
  currencyDisplay : 'symbol',
  useGrouping     : true
} ) + "<br>";
result += number.toLocaleString( [ 'jav', 'en' ], { 
  localeMatcher            : 'lookup',
  style                    : 'decimal',
  minimumIntegerDigits     : 2,
  minimumFractionDigits    : 2,
  maximumFractionDigits    : 3,
  minimumSignificantDigits : 2,
  maximumSignificantDigits : 3
} ) + "<br>";

var el = document.getElementById( 'result' );
el.innerHTML = result;

<div id="result"></div>

Details on the MDN info page.

Edit: Commentor @I like Serena adds the following:

To support browsers with a non-English locale where we still want English formatting, use value.toLocaleString('en'). Also works for floating point.

Lots of good answers already. Here's another, just for fun:

function format(num, fix) {
    var p = num.toFixed(fix).split(".");
    return p[0].split("").reduceRight(function(acc, num, i, orig) {
        if ("-" === num && 0 === i) {
            return num + acc;
        }
        var pos = orig.length - i - 1
        return  num + (pos && !(pos % 3) ? "," : "") + acc;
    }, "") + (p[1] ? "." + p[1] : "");
}

Some examples:

format(77.03453, 2); // "77.03"
format(78436589374); // "78,436,589,374"
format(784, 4);      // "784.0000"
format(-123456);     // "-123,456"

Lots of good answers already. Here's another, just for fun:

function format(num, fix) {
    var p = num.toFixed(fix).split(".");
    return p[0].split("").reduceRight(function(acc, num, i, orig) {
        if ("-" === num && 0 === i) {
            return num + acc;
        }
        var pos = orig.length - i - 1
        return  num + (pos && !(pos % 3) ? "," : "") + acc;
    }, "") + (p[1] ? "." + p[1] : "");
}

Some examples:

format(77.03453, 2); // "77.03"
format(78436589374); // "78,436,589,374"
format(784, 4);      // "784.0000"
format(-123456);     // "-123,456"

Ok I have posted answer below. I have added limit of 20 numbers. You can change it as per your need.

You can use Number.toLocaleString() for this purpose.

Below is working example:

// When ready.
$(function() {
  var extra = 0;
  var $input = $("#amount");

  $input.on("keyup", function(event) {

    // When user select text in the document, also abort.
    var selection = window.getSelection().toString();
    if (selection !== '') {
      return;
    }

    // When the arrow keys are pressed, abort.
    if ($.inArray(event.keyCode, [38, 40, 37, 39]) !== -1) {
      if (event.keyCode == 38) {
        extra = 1000;
      } else if (event.keyCode == 40) {
        extra = -1000;
      } else {
        return;
      }

    }

    var $this = $(this);
    // Get the value.
    var input = $this.val();
    var input = input.replace(/[\D\s\._\-]+/g, "");
    input = input ? parseInt(input, 10) : 0;
    input += extra;
    extra = 0;
    $this.val(function() {
      return (input === 0) ? "" : input.toLocaleString("en-US");
    });
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input id="amount" name="amount" type="text" maxlength="20" />