Question

This does not seem to be working I am not sure how to get this while loop to work correctly any help would be appreciated.

function getProductCode() {
   productCode = parseInt(prompt("Enter Product Code: "));
   while (productCode < 1 || > 9999) 
   {
      document.writeln("Error! the product Code must be between 1 - 9999");
      parseInt(prompt("Enter Product Code: "));
   }
   return productCode
}

getProductCode()

Answer 1

You’re missing an operand (productCode) at the left side:

while (productCode < 1 || productCode > 9999) 
                          ^^^^^^^^^^^

And:

• Supply a radix to parseInt. When unspecified, 010 becomes 8 (octal literal).
• Do not leak variables to the global scope, use var to declare local variables.
• Invert your logic, or use isNaN. When an invalid number is supplied (NaN), your loop should not stop.
• It’s better to move the message from document.writeln to the dialog.
• Assign the new value to productCode. Otherwise, you won’t get far…
• Important: Dialogs can be disabled in browsers. Do not loop infinitely many times, but add a treshold.

Final code which takes care of the first 5 bullet points:

function getProductCode() {
   var productCode = parseInt(prompt("Enter Product Code: "), 10);
   while (!(productCode >= 1 && productCode <= 9999)) {
      productCode = parseInt(prompt("Error! the product Code must be between 1 - 9999\nEnter Product Code: "), 10);
   }
   return productCode;
}

I have not implemented the treshold, it’s up to you to do that.