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

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;
}

Update 2019 5 years after this answer was written, a solution was standardized in ECMA Script 2015. That solution is covered in this answer.

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:

There is a method called Number.isInteger() which is currently implemented in everything but IE. MDN also provides a polyfill for other browsers:

Number.isInteger = Number.isInteger || function(value) {
  return typeof value === 'number' && 
    isFinite(value) && 
    Math.floor(value) === value;
};

However, for most uses cases, you are better off using Number.isSafeInteger which also checks if the value is so high/low that any decimal places would have been lost anyway. MDN has a polyfil for this as well. (You also need the isInteger pollyfill above.)

if (!Number.MAX_SAFE_INTEGER) {
    Number.MAX_SAFE_INTEGER = 9007199254740991; // Math.pow(2, 53) - 1;
}
Number.isSafeInteger = Number.isSafeInteger || function (value) {
   return Number.isInteger(value) && Math.abs(value) <= Number.MAX_SAFE_INTEGER;
};

Solution 4:

Why not something like this:

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

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!