function checkNumeric(objName)
  {
    var lstLetters = objName;

    var lstReplace = lstLetters.replace(/,/g,'');
  }

<input type="text" onblur="checkNumeric(this);" name="nocomma" size="10" maxlength="10"/>

var rawstring = '1,200,000';
var cleanstring = rawstring.replace(/[^d.- ]/g, '');

1234 --> 1234
1,234 --> 1234
-1234 --> -1234
-1,234 --> -1234
1234.5 --> 1234.5
1,234.5 --> 1234.5
-1,234.5 --> -1234.5
1xxx234 --> 1234

function unComma( val, dec )
{
    var newVal		= 0,
    	defaultVal	= 0,
    	dec		= (dec || 2);

    if ( !val )
    	return defaultVal;

    val = val.toString().replace(/,/g, '');

    if ( !val )
    	return defaultVal;

    newVal = parseFloat(val);

    if ( isNaN(newVal) )
    	return defaultVal;

    newVal = +( newVal.toFixed(dec) );

    return ( newVal || defaultVal );
}