How to validate whether a variable is valid integer allowing +/-? in pure javascript

Question

I need to validate whether a input is a valid integer allowing for +/- entries.

I have tried this.

 function valid(elem)
 { 
      var num = parseInt(elem);
      if(!Number.isInteger(num))
      {
         alert ("Not an integer");
      }
 }

But the issue here is , it is validating even strings like 10sd as an integer. So how to validate this?

I want to validate as following:

valid(-10) = true;
valid(+10) = true;
valid(-10.01) = false;
valid(10sd) = false;
valid(10.23see) = false;
valid(10) = true;

Is hexadecimal, octal or binary input valid? Depending on what you consider valid, a regular expression might be the simplest approach. — Felix Kling, Nov 21 '19 at 10:56
@NickParsons: That alone is not enough. `isNaN("5.5")` is `false`. — Felix Kling, Nov 21 '19 at 10:57
With "plain numbers" I assume you mean decimal numbers. Is the input a string or a number? Do you want it to accept strings? (I assumed since you use `parseInt` but I'm not sure anymore; it's also unclear whether +/- just means positive or negative numbers or whether a string can start with + or -). — Felix Kling, Nov 21 '19 at 11:02
@FelixKling the input varies it can be string/number/decimal, i want to validate whether it is an integer. For ex. +10 and -10 is valid while 10sd or -10se aren't — AriiNkhun, Nov 21 '19 at 11:05
You probably want `Number.isInteger(Number(elem))`, but note that a string `"0xa"` would be valid, since it's a valid hexadecimal number. Alternatively: `typeof elem !== 'number' && /^[+-]?\d+$/.test(elem) || Number.isInteger(elem)` — Felix Kling, Nov 21 '19 at 11:07
@FelixKling your answer works great and solves my issue. Thanks for your time. Can you please put is as an answer so that i can upvote? — AriiNkhun, Nov 21 '19 at 11:14

Shashank Gandham · Answer 1 · 2019-11-21T13:49:48.590

0

function valid(value) {
   if(typeof value === 'number' && isFinite(value))
       alert ("It is an integer");
}

This function does the job, typeof is a keyword in Javascript which tells you the data type of the variable

Edit: made a silly error in alert, it should alert if it is an integer, the if condition checks for number

edited Nov 21 '19 at 13:49

answered Nov 21 '19 at 10:59

Shashank Gandham

Dusan Krstic · Answer 2 · 2019-11-21T11:10:02.163

0

Simple

function valid(elem){return parseInt(elem)==elem}

edited Nov 21 '19 at 11:10

answered Nov 21 '19 at 11:01

Dusan Krstic

If you already know that a value is a number (`typeof elem=="number"`) why do you use `parseInt`? `parseInt` converts strings to numbers. – Felix Kling Nov 21 '19 at 11:05
We need to determine if it is an integer. in fact, this is enough for this task, so the function can only be: function valid(elem){return parseInt(elem)==elem} – Dusan Krstic Nov 21 '19 at 11:06
Then I would suggest `Math.floor(elem) === elem` instead. Of course the whole function can be replaced with `Number.isInteger` instead. – Felix Kling Nov 21 '19 at 11:09

2 Answers2