Javascript Prompt/textbox Only Numbers

Hey guys I'm just learning javascript, I have some html and css background though. I can't figure out how to allow only number values to be entered into a prompt, or check if its a

Solution 1:

here is a good number testing function I use in a bit of my code (from Validate decimal numbers in JavaScript - IsNumeric()). It will return true if number, false if not. This is floating point validation, not integer

function isNumber(n) {
  return !isNaN(parseFloat(n)) && isFinite(n);
}

Solution 2:

You already have a good answer. This answer is another look at things you can do.

Assuming your number field is like the following

<input type="text" name="num_fld" id="num_fld" onchange="return chkNum();" />

and you've defined a javascript function like so

function chkNum()
{
   var rc = false;

   if(!isNaN(parseFloat(n)) && isFinite(n))
   {
     rc = true;
   }
   else
   {
      document.getElementById("num_fld").value = 0;
   }
   return rc;
}

This function checks to see if the number is really a number, but also monkeys with the input, so the bad value does not stay in place. Offhand I am not quite sure if returning false prevents the number from being entered (kind of like in a validate function.) I believe from my testing that returning false does affect what is in the field, but I am not 100% sure of that.

You could also alter the background and/or text color of the input field upon failure (the else part of the test, so the user notices something is wrong. alert(); is good for testing, but kind of messes up the look of your site in production.