Using a custom renderer function in ExtJS4 to properly handle currency rounding

example.js

/*Uses https://github.com/MikeMcl/big.js/
to allow for arbitrary decimal precision and
get away from floating point inaccuracy
*/

{
  xtype     : 'numbercolumn',
  header    : 'Price',
	dataIndex : 'line_item_price',
	renderer  : function( v ) {
		return '$' + Big( v ).toFixed(2);
	}
}

// The example number is 20.775
// Calling this renderer with v = 20.775
// returns "$20.78" as expected.