How can I check if a string is a float?

Question

I am passing in a parameter called value. I'd like to know if value is a float. So far, I have the following:

if (!isNaN(value))
{
    alert('this is a numeric value but not sure if it is a float.');
}

How do I go one step further and convert the string to something that can evaluate to a float?

Answer 1

Like this:

if (!isNaN(value) && value.toString().indexOf('.') != -1)
{
    alert('this is a numeric value and I\'m sure it is a float.');
}​

Answer 2

You can use the parseFloat function.

If the value passed begins with what looks like a float, the function returns the value converted to a float, otherwise it will return NaN.

Something like:

function beginsWithFloat(val) {
  val = parseFloat(val);
  return ! isNaN(val);
}
console.log(beginsWithFloat("blabla")); // shows false
console.log(beginsWithFloat("123blabla")); // shows true

Answer 3

Following functions also check for format. E.g. JavaScript native parseInt and parseFloat functions also parse strings containing non numeric characters, and functions above have consequences of this.

// For example, following code will work
var n = parseInt('123asd');
n == 123

These functions will return false for such string.

function isFloat(val) {
    var floatRegex = /^-?\d+(?:[.,]\d*?)?$/;
    if (!floatRegex.test(val))
        return false;

    val = parseFloat(val);
    if (isNaN(val))
        return false;
    return true;
}

function isInt(val) {
    var intRegex = /^-?\d+$/;
    if (!intRegex.test(val))
        return false;

    var intVal = parseInt(val, 10);
    return parseFloat(val) == intVal && !isNaN(intVal);
}

Answer 4

To check if a string is an integer or a float

function isFloat(n) {
    return parseFloat(n.match(/^-?\d*(\.\d+)?$/))>0;
}

//alert(isFloat("3.444"));

Answer 5

In my case a very simple regex did the trick.

I needed to validate an user's input whether the input is a valid monetary value. I simply used-

/^[0-9]+(\.)?[0-9]*$/.test(number)

everything between // is the Regular Expression.

/^ means the match starts from the beginning of the word and $/ means the match ends with the word. If you think the word can not start with the letter 0 then the expression would be like [1-9][0-9]*

[0-9]+ means the word must start with at least one number.

Note: * means zero or more, + means one or more and ? means one or none.

Up to here the expression is /^[1-9][0-9]*$/ and this would validate only the integer numbers.

To test for a period (.) in the number we need to use \. with the expression. . is a special character which matches everything, \. will only match the period.

Finally another character class [0-9]* would match with zero or more digits.

Test Cases

/^[0-9]+(\.)?[0-9]$/.test("21.38a") // ==> false
/^[0-9]+(\.)?[0-9]$/.test("21.38") // ==> true
/^[0-9]+(\.)?[0-9]$/.test("y2781.68") // ==> false
/^[0-9]+(\.)?[0-9]$/.test("2781r.68") // ==> false

Answer 6

Number.prototype.isFloat = function() {
    return (this % 1 != 0);
}

Then you can

var floatValue = parseFloat("2.13");
var nonFloatValue = parseFloat("11");

console.log(floatValue.isFloat()); // will output true
console.log(nonFloatValue.isFloat()); // will output false

Values like 2.00 cannot really be considered float in JS, or rather every number is a float in JS.

---

EDIT: Forgot to mention that extending the prototypes of built-in types is considered a bad parctice (for a good reason) and its use is discouraged in production environments. You could still implement this check as a plain function

Answer 7

Use This:

var isNumber = /^\d+\.\d+$/.test(value);

Answer 8

function checkFloat(value) {
    let parsed = Number.parseFloat(value);
    return (!Number.isNaN(parsed)) && (!Number.isInteger(parsed))
}

Answer 9

To check if a string is a float (avoid int values)

function isFloat(n) {
   if( n.match(/^-?\d*(\.\d+)?$/) && !isNaN(parseFloat(n)) && (n%1!=0) )
      return true;
   return false;
}

var nonfloat = isFloat('12'); //will return false
var nonfloat = isFloat('12.34abc'); //will return false
var float = isFloat('12.34'); //will return true

Answer 10

Only if value is passed in as a string can we fully determine if it uses a decimal point or not. Because 1.0 (as a number) results in 1 though "1.0" (as a string) results in "1.0" exactly the same. And from there we can find if it contains a decimal point, .. So we need to pass the argument value as a string.

_{The following will work if value is a string}

if ( value.indexOf('.') > -1 ) { // value is a floating point

}

value.toString() will not turn 1.0 to "1.0" (rather, it would simply turn it to 1) so passing by string is the best alternative because it maintains all of its characters.

If you do not wish to use a string, then there is no way of capturing 1.0 as a floating-point value. Use the following if you want to test of a number is a floating point value:

_{The following will not work for 1.0, 1.00, etc.}

if ( value >>> 0 !== x ) { // value is a floating point

}

Note: You should also check for !isNaN(value) (I left that out to focus on the changes).

Answer 11

If you need to check if value is int or float:

function isFloatOrInt(n) {
    return !isNaN(n) && n.toString().match(/^-?\d*(\.\d+)?$/);
}

Answer 12

This function returns the numeric value of a string regardless if int or float

function getNumericVal(str) {
    if(isNaN(str)) return;
    try {return parseFloat(str);} 
    catch(e) {return parseInt(str);}
}

Answer 13

use this jquery code

    <script>
    $(document).ready(function () {
        $(".allow_only_float").keypress(function (e) {

            if (e.which != 46 && e.which != 8 && e.which != 0 && (e.which < 48 || e.which > 57)) {
                e.preventDefault();//return false;
            }
            var avg = $('#<%=txtAverage.ClientID%>').val();
            var idx = avg.indexOf(".");
            if (idx > -1 && e.which == 46) {
                e.preventDefault();//return false;
            }
        });
    });
    </script>
<body>
    <input type='text' class='allow_only_float'>
</body>

Answer 14

function isFloat(inputString) {
    const parsed = parseFloat(inputString);

    return !isNaN(parsed) && parsed.toString() === inputString;
}

isFloat('.4') // false
isFloat('1.4') // true
isFloat('1.') // false
isFloat('1') // true
isFloat('asd') // false
isFloat('123asd') // false

Answer 15

In may cases this is enough

function isFloat(n) {
    return (typeof n === 'number' && !isNaN(n) && n !== Infinity && n !== -Infinity) || (typeof n === 'string' && /^\-?[0-9]+(e[0-9]+)?(\.[0-9]+)?$/.test(n));
}

Answer 16

straight forward:

if (parseFloat(value).toString() === value.toString()) {
    ...
}

Answer 17

if (!isNaN(value) && String(value).includes('.')) {
    alert("it's a float");
    let newFloatValue = parseFloat(value)
}