How to reject an invalid string for userinput in javascript

Question

I need help with rejecting an invalid string in JS:

I want to ensure any input other than the numbers 1-6 is rejected e.g 0 or 7+ or any other character, here is what i got so far

function getGraph() {
  var i;
  var results = [];
  var dicePoss = [1, 2, 3, 4, 5, 6]
  var tracker;

  for (i = 1; i <= 30; i++) {
    tracker = parseInt(results.push(prompt("Enter your numbers", 'diceroll')));

  }

  if (tracker <= 6 && tracker > 0) {
    document.getElementById('x-axis').innerHTML = tracker;
  } else {
    document.getElementById('reject').innerHTML = "Please enter a numberPlease enter a valid number between 1-6";
  }

  document.getElementById('y-axis').innerHTML = dicePoss;
}

<!DOCTYPE html>

<html>

<body>

  <p id="y-axis">Frequency of die rolls(results)</p>
  <p id="x-axis">Dice Possible Rolls between 1-6</p>
  <p id="reject"></p>

  <input type="button" value="Graph Column Chat for Dice Roll" onclick="getGraph();">
</body>

</html>

Please write a Minimal, Complete, and Verifiable Example. It's not nice to make someone trying your snippet go through 30 popups just to test your code. — Federico klez Culloca
– Federico klez Culloca, Commented Feb 11, 2019 at 13:50

jcubic · Accepted Answer · 2019-02-11 19:25:13Z

2

To fix the issue you can use regular expressions:

var str = prompt("Enter your numbers",'diceroll');

if (str.match(/^[1-6]$/)) {
   results.push(str);
} else {
   // show error
}

And some comment about your code, you have this:

for (i = 1; i <= 30; i++) {
    tracker = parseInt(results.push(prompt("Enter your numbers", 'diceroll')));

}

which is wrong in two ways:

first it will parse result of push which is index (number) of last pushed value.
and second is that the value will be last push (tracker === 30).

In my code the check goes inside the loop, not outside of it.

edited Feb 11, 2019 at 19:25

answered Feb 11, 2019 at 14:03

jcubic

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