Validação de CPF

<script type="text/javascript">
				document.getElementById('username').onblur = function validarCPF(cpf){
					var cpf = document.getElementById('username').value;
					var cpfStr = cpf.toString();
					 if(cpfStr.length != 11 || cpfStr.replace(eval('/'+cpfStr.charAt(1)+'/g'),'') == '')
					 {
							alert('CPF inválido');
					 }
					 else
					 {
							for(n=9; n<11; n++)
							{
								 for(d=0, c=0; c<n; c++) d += cpfStr.charAt(c) * ((n + 1) - c);
								 d = ((10 * d) % 11) % 10;
								 if(cpfStr.charAt(c) != d) return false;
							}
							return true;
					 }
					}
				</script>