Spiral 2 – how to validate data with Dart

If you have tested the Spiral 1 – the power of HTML5 forms version thoroughly, you would have come across some things that could be improved:

1. The HTML5 control only does its checks when the Create Account button is clicked on; it would be better if the user is alerted earlier, preferably after filling in each field.
2. The Birth Date value is checked to be a correct DateTime value, but a value in the future is accepted.
3. The Gender field will gladly accept other values than M or F.
4. The Balance field accepts a negative number.

So HTML5 doesn't give us full validation possibilities; to remedy and supplement that, we must add code validation, see bank_terminal_s2.dart:

Note

For code files of this section, refer to chapter 6\bank_terminal_s2 in the code bundle.

InputElement name, address, email, birth_date, gender;
InputElement number, balance, pin_code;
void main() {
  // bind variables to DOM elements:
  name = querySelector('#name&apos...