A simple function, the basis of was in the public domain (see comments) to format a number with thousand separators.

 

Ext.apply(Ext.util.Format,{
 
    decimalSeparator : '.',
    thousandSeparator : ',',
        
    /* Adapted from http://www.mredkj.com/javascript/nfbasic.html, 
     * Public Domain, without copyright, and can be used without restriction: 
     * see http://www.mredkj.com/legal.html
     */    
    asThousands : function(value)
    {
        value = parseInt(value,10) + '';
        var x = value.split(this.decimalSeparator);
        var x1 = x[0];
        var x2 = x.length > 1 ? this.decimalSeparator + x[1] : '';
        var rgx = /(\d+)(\d{3})/;
        while (rgx.test(x1)) {
            x1 = x1.replace(rgx, '$1' + this.thousandSeparator + '$2');
        }
        return x1 + x2;
    }
});