Javascript; valid input based on a range of numbers

Question

I need to validate a user input for a GPA calculator based on the following criteria:

Is a number
Is an integer value between 3 and 7, or 1.5 floating point value.

So far I have tried the following:

var gradeInputMessage = "Please enter your  grade for course " +userInput;
var gradeInput = "";

gradeInput = prompt(gradeInputMessage);

while (
  isNaN(gradeInput) || //grade input is a number
      gradeInput <3 || gradeInput >7
)
{
alert ("invalid Course Grade. Please try again");
gradeInput = prompt(gradeInputMessage);
}

This seems to work fine for the numbers 3,4,5,6,7, but I have no idea how to include 1.5

Please excuse any ignorance on my behalf, this is a university course that I have to complete, and I have never done any form of programming, nor do I do any for work.

Appreciate any help/feedback.

Cheers, Mitchell

you could use an if statement separately just before the while to check "if(gradeInput == 1.5)". do you intend to return some data or do you have some code below the while loop? — Ousmane D.
– Ousmane D., Commented Apr 18, 2017 at 1:20
@Hamms— === won't work, the value returned by prompt is a string. ;-) — RobG
– RobG, Commented Apr 18, 2017 at 1:34
ah, true! In that case, <3 and >7 are also going to work unexpectedly, and OP is going to want to throw in a gradeInput = Number(gradeInput) somewhere — Hamms
– Hamms, Commented Apr 18, 2017 at 1:38

A. L · Accepted Answer · 2017-04-18 01:47:29Z

2

Probably easier to just check for the things that you want, then not them.

Also added a null checker so people can hit cancel to exit out of the prompt loop.

And I convert the string into a number by putting + in front of gradeInput

var gradeInputMessage = "Please enter your  grade for course ";

var gradeInput = prompt(gradeInputMessage);

while (
  gradeInput !== null &&
  (
  isNaN(gradeInput) || //grade input is a number
      !((+gradeInput >=3 && +gradeInput <=7) || +gradeInput === 1.5)
  )
)
{
alert ("invalid Course Grade. Please try again");
gradeInput = prompt(gradeInputMessage);
}

edited Apr 18, 2017 at 1:47

answered Apr 18, 2017 at 1:39

A. L

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2 Comments

Hamms Over a year ago

as @RobG pointed out, you'll want to make sure to convert the result of prompt to a number before check it

A. L Over a year ago

@Hamms ah, yes, I added Number to the bottom, but forgot the top, I could also just do with soft checking :\

Dalin Huang · Accepted Answer · 2017-04-18 01:35:25Z

Are you doing a web app?

html 5 with type="number" input can valid the number for you.

I'm using jQuery here but it can be done in pure js easily. also validGpa.indexOf(gpa) this is pure js (.indexOf())

my example here use an Array to save all valid GPA, if any input match then print msg xx is valid. If not matching, say 'Sorry ...'

var validGpa = ['3', '4', '5', '6', '7', '1.5'];
$('#inputgpa').on('change', function() {
  var gpa = $(this).val();
  if (validGpa.indexOf(gpa) > -1) {
    $('#validation').text(gpa + ' is Valid!');
  } else {
    $('#validation').text('Sorry! ->' + gpa + '<- is not a valid GPA...');
  }
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>

<span>Enter your GPA now:<span><br>
<input id="inputgpa" type="number" /><br>
<span id="validation"></span>

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