Validate if a value is a whole number [duplicate]

Question

I don't think isNaN is gonna work for my situation. I want to make sure a certain variable only contains whole numbers when I validate it. So -1.45 in my case should not be allowed. Values such as 1, 23, 334 should be allowed/valid.

Answer 1

PART #1:

You can use remainder operator to find if a value is whole number or not like:

function isWholeNumber(value) {
  if (value % 1 === 0) {
    console.log(value + ' is a whole number');
  } else {
    console.log(value + ' is not a whole number');
  }
}

// Display the result here
isWholeNumber(1.45);
isWholeNumber(23);

Explanation:

• The remainder operator returns the remainder left over when one operand is divided by a second operand.
• For example, 1.45 % 1 returns 0.44999999999999996 and 23 % 1 returns 0.
• So, now if a value % 1 === 0, then we can say that value is a whole number else not.

---

PART #2:

This logic fails in some cases where value is not actually a number, as remainder operator (%) converts its operands to numbers like:

function isWholeNumber(value) {
  console.log(value % 1); //<--- result is always 0
  if (value % 1 === 0) {
    console.log(value + ' is a whole number');
  } else {
    console.log(value + ' is not a whole number');
  }
}

// Display the result here
isWholeNumber('23');
isWholeNumber('');
isWholeNumber(true);

This result in a display of incorrect results like empty string and boolean value display as the whole number. We can fix this by checking of type of value is number like:

function isWholeNumber(value) {
  if (typeof value === 'number' && value % 1 === 0) {
    console.log(value + ' is a whole number');
  } else {
    console.log(value + ' is not a whole number');
  }
}

// Display the result here
isWholeNumber(1.45);
isWholeNumber(24);
isWholeNumber('23');
isWholeNumber('');
isWholeNumber(true);

---

PART #3:

In ES6 global object Number got a new property Number.isInteger(value). It checks whether value is a whole number like:

// Display the result here
console.log(Number.isInteger(1.45));
console.log(Number.isInteger(24));
console.log(Number.isInteger('23'));
console.log(Number.isInteger(''));
console.log(Number.isInteger(true));

We can integrate this with our modified isWholeNumber function in part #2 like:

function isWholeNumber(value) {
  if (Number.isInteger(value)) {
    console.log(value + ' is a whole number');
  } else {
    console.log(value + ' is not a whole number');
  }
}

// Display the result here
isWholeNumber(1.45);
isWholeNumber(24);
isWholeNumber('23');
isWholeNumber('');
isWholeNumber(true);

Answer 2

isNaN() is to check number or not .It will not check the number is whole or not.

function isInt(n) {
   return n % 1 === 0;
}

or

if (number % 1 == 0) {
    alert('Whole Number');
} else {
    alert('Not a Whole Number');
}