Number validation in JavaScript

var

customerNumberInput = document.getElementById("customerNumber");

var customerNumber = customerNumberInput != null ? customerNumberInput.value : "";

//Added for FY12 Enhancements changes by BM54284

if(customerNumber){

customerNumber= customerNumber.replace(

/^\s+|\s+$/, '');

if(isNaN(customerNumber) == true)

return warnInvalid(customerNumberInput, "Please provide Numeric value for Customer Number.");

if(customerNumber.length != 9)

return warnInvalid(customerNumberInput, "Please provide the valid Customer Number.");

}