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

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
– Felix Kling, Commented Nov 21, 2019 at 10:56
@NickParsons: That alone is not enough. isNaN("5.5") is false. — Felix Kling
– Felix Kling, Commented Nov 21, 2019 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
– Felix Kling, Commented Nov 21, 2019 at 11:02

Dusan Krstic · Accepted Answer · 2019-11-21 11:10:02Z

0

Simple

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

edited Nov 21, 2019 at 11:10

answered Nov 21, 2019 at 11:01

Dusan Krstic

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3 Comments

Felix Kling Over a year ago

If you already know that a value is a number (typeof elem=="number") why do you use parseInt? parseInt converts strings to numbers.

Dusan Krstic Over a year ago

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}

Felix Kling Over a year ago

Then I would suggest Math.floor(elem) === elem instead. Of course the whole function can be replaced with Number.isInteger instead.

Shashank Gandham · Accepted Answer · 2019-11-21 13:49:48Z

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

You can check this out, for more usage of typeof: https://webbjocke.com/javascript-check-data-types/

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

edited Nov 21, 2019 at 13:49

answered Nov 21, 2019 at 10:59

Shashank Gandham

36 bronze badges

2 Comments

Felix Kling Over a year ago

valid(5) says "Not an integer".

Shashank Gandham Over a year ago

Sorry for the error, answer updated

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