Random Passwords on Demand

Listing 2: The generate Function

// Executes when the Generate Passwords button is clicked.
function generate() {
  var chars, len, num, m, n, pwds, pwd;

  // Build a string based on the check boxes.
  chars = "";
  if (id("uppercase").checked) chars += UPPER_CHARS;
  if (id("lowercase").checked) chars += LOWER_CHARS;
  if (id("numbers").checked)   chars += NUMBER_CHARS;
  if (id("symbols").checked)   chars += SYMBOL_CHARS;

  // Complain if none of the check boxes are selected.
  if (chars == "") {
    window.alert("Select at least one character class.");
    id("uppercase").focus();
    event.returnValue = false;
    return;
  }

  // Parse the password length field as base 10 number. Complain
  // if the value is not a number or outside the allowed range.
  len = parseInt(id("len").value, 10);
  if (isNaN(len) || (len < 1) || (len > MAX_PASSWORD_LENGTH)) {
    window.alert("Enter a number in the range 1 to " +
      MAX_PASSWORD_LENGTH + ".");
    event.returnValue = false;
    id("len").focus();
    return;
  }

  // Parse the number of passwords field as a base 10 number. Complain
  // if the value is not a number or outside the allowed range.
  num = parseInt(id("num").value, 10);
  if (isNaN(num) || (num < 1) || (num > MAX_PASSWORD_NUMBER)) {
    window.alert("Enter number in the range 1 to " +
      MAX_PASSWORD_NUMBER + ".");
    event.returnValue = false;
    id("num").focus();
    return;
  }

  // Clear the list of passwords.
  id("passwords").value = "";

  // The pwds variable will contain a newline-delimited list of
  // random passwords. The code generates a random password, stores
  // it in the pwd variable, and appends it to the pwds variable.
  pwds = "";
  for (m = 0; m < num; m++) {

// Begin Callout A
    pwd = "";
    for (n = 0; n < len; n++)
      pwd += chars.charAt(Math.floor(Math.random() * chars.length));
// End Callout A

// Begin Callout B
    pwds += pwds == "" ? pwd : "\n" + pwd;
// End Callout B
  }

  // Update the password list and enable the Copy to Clipboard and
  // Clear List buttons.

// Begin Callout C
  id("passwords").value = pwds;
  id("copydata").disabled = false;
  id("clear").disabled = false;
// End Callout C
}