Validate Negative Number

Question

I'm looking to make a new function that will validate the field but allow for negative numbers aswell as positive e.g. =/- 999.99 . Would anyone have a quick and easy solution. Thanks

function validateNumber(thenumber){
    try{
        validnumbers = "0123456789.,";
    valid = false;
    for(i=0;i<thenumber.length;i++){
       if (validnumbers.indexOf(thenumber.charAt(i)) == -1)
       {
          valid = false;
          break;
       }
       else
          valid = true;
    }
    return valid;
    }catch(e){}
   }

You might be better off to use a RegExp http://stackoverflow.com/questions/16460773/regex-validate-negative-and-positive-decimal-numbers — htatche, Jul 20 '15 at 14:45

score 7 · Accepted Answer · answered Jul 20 '15 at 14:47

7

What about this simple function?

function validateNumber(thenumber)
{
    thenumber = thenumber.replace(".", "").replace(",", ".");

    return !isNaN(thenumber);
}

Fiddle

The function removes dots then replaces comma with dots. Then it uses isNaN with negation to return if its valid or not. You may want to add a check if thenumber is a string to prevent runtime errors.

answered Jul 20 '15 at 14:47

DontVoteMeDown

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@topcat3, why the snarky comment? If the answer does not meet your needs, kindly explain why. – Sparky Jul 20 '15 at 15:41
@DontVoteMeDown no snarky comment. your help was greatly appreciated. – topcat3 Jul 22 '15 at 10:31

AmmarCSE · Answer 2 · 2015-07-20T14:53:27.360

2

Use isNaN

function validateNumber(thenumber){
    return !isNaN(thenumber);
   }

isNaN will return false for both positive and negative numbers

edited Jul 20 '15 at 14:53

answered Jul 20 '15 at 14:47

AmmarCSE

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@Jongware, no it does not. Have you tried it? I have – AmmarCSE Jul 20 '15 at 14:48
Is parseInt really needed ? Or could it lead to unexpected results in some edge-cases ? – htatche Jul 20 '15 at 14:52
I have a question: Why this `!isNaN(parseInt("13.12313,123dasd.asd1"))` is evaluating to `true` ? – DontVoteMeDown Jul 20 '15 at 14:54

score 1 · Answer 3 · answered Jul 20 '15 at 15:23

I think the better way to do this is using regular expresions: The search() method uses an expression to search for a match, and returns the position of the match(return -1 in other case).Here is an example:

public function validNumber(number)
{
    return number.search("^[+-]?[0-9]{1,9}(?:\.[0-9]{1,2})?$") > 0;
}

num8er · Answer 4 · 2015-07-20T15:07:13.117

0

try this:

function isNumber(value) {
  value = value.replace(',', '.');
  return !isNaN(value);
}

function isNegative(value) {
  return (isNumber(value) && value<0);
}

function isPositive(value) {
  return (isNumber(value) && value>0);
}

and as bonus (:

function isNumberWithDots(value) {
  value = value.split(',').join('').split('.').join('');
  return !isNaN(value);
}

edited Jul 20 '15 at 15:07

answered Jul 20 '15 at 14:47

num8er

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*" negative numbers aswell as positive"*. – Spencer Wieczorek Jul 20 '15 at 14:48
I believe your `isNumber` function may return wrong value. E.g.: If you try to check `12.123,12` it will become `12.123.12` and `isNumber` will return false. It is ok, but in fact the number was valid, right? – DontVoteMeDown Jul 20 '15 at 14:57
1

of course 12.123.12 is not number, 12.12312 is number. – num8er Jul 20 '15 at 15:05
added function as bonus :) – num8er Jul 20 '15 at 15:07
@DontVoteMeDown, since when are `12.123,12` or `12.123.12` valid numbers? – Sparky Jul 20 '15 at 15:40
sorry not looked at who's writing :) – num8er Jul 20 '15 at 15:50
@Sparky in my culture(pt-br) `12.123,12` is a valid number, and it may be valid in another culture, since OP didn't specified a culture. – DontVoteMeDown Jul 20 '15 at 16:52
@num8er `12.123.12` maybe invalid, but what I said is if you try to check for `12.123,12` your function will check as `12.123.12`, what changes everything. – DontVoteMeDown Jul 20 '15 at 16:53

score 0 · Answer 5 · edited May 23 '17 at 12:31

0

Try this expression:

(number < 0)

It will be evaluated by JavaScript by first attempting to convert the left hand side to a number value.

Further details can be found here:

Javascript negative number

Conversely, this expression:

(number > 0)

will be evaluated by JavaScript in the same manner.

edited May 23 '17 at 12:31

Community

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answered Jul 20 '15 at 14:52

Daniel Burgner

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He also wants to validate positive numbers. – htatche Jul 20 '15 at 14:53

Validate Negative Number

5 Answers5