How do I check that a number is float or integer?

How do I check that a number is float or integer?

How to find that a number is float or integer?
1.25 –> float
1 –> integer
0 –> integer
0.25 –> float

Solutions/Answers:

Solution 1:

check for a remainder when dividing by 1:

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

If you don’t know that the argument is a number you need two tests:

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

function isFloat(n){
    return Number(n) === n && n % 1 !== 0;
}

Solution 2:

Try these functions to test whether a value is a number primitive value that has no fractional part and is within the size limits of what can be represented as an exact integer.

function isFloat(n) {
    return n === +n && n !== (n|0);
}

function isInteger(n) {
    return n === +n && n === (n|0);
}

Solution 3:

Why not something like this:

var isInt = function(n) { return parseInt(n) === n };

Solution 4:

There is a method called Number.isInteger() which is currently implemented only in latest Firefox and is still a part of EcmaScript 6 proposal. However MDN provides a polyfill for the other browsers, which matches the one specified in ECMA harmony:

if (!Number.isInteger) {
  Number.isInteger = function isInteger (nVal) {
    return typeof nVal === "number" && isFinite(nVal) && nVal > -9007199254740992 && nVal < 9007199254740992 && Math.floor(nVal) === nVal;
  };
}

Solution 5:

You can use a simple regular expression:

function isInt(value) {

    var er = /^-?[0-9]+$/;

    return er.test(value);
}

Or you can use the below functions too, according your needs. They are developed by the PHPJS Project.

is_int() => Check if variable type is integer and if its content is integer

is_float() => Check if variable type is float and if its content is float

ctype_digit() => Check if variable type is string and if its content has only decimal digits

Update 1

Now it checks negative numbers too, thanks for @ChrisBartley comment!

Solution 6:

Here are efficient functions that check if the value is a number or can be safely converted to a number:

function isNumber(value) {
    if ((undefined === value) || (null === value)) {
        return false;
    }
    if (typeof value == 'number') {
        return true;
    }
    return !isNaN(value - 0);
}

And for integers (would return false if the value is a float):

function isInteger(value) {
    if ((undefined === value) || (null === value)) {
        return false;
    }
    return value % 1 == 0;
}

The efficiency here is that parseInt (or parseNumber) are avoided when the value already is a number. Both parsing functions always convert to string first and then attempt to parse that string, which would be a waste if the value already is a number.

Thank you to the other posts here for providing further ideas for optimization!