How to validate an input as an number in JavaScript

Question

I'm new with JavaScript programming and have been trying to validate a number that is inputted from a user on a php page. Here is the javascript that is included.

var validate_and_create = function(){
    var i_number = $("input_number").value;
    var isValid = true;

    if (i_number === ""){
        $("create_n_error").firstChild.nodeValue = "Number text field cannot be blank.";
        isValid = false;
    } else {
        if  (typeof i_number === 'number') {
            $("create_n_error").firstChild.nodeValue = "This is a number!";
            isValid = true;
        } else {
            $("create_n_error").firstChild.nodeValue = "This is not a number!";
            isValid = false;
        }
    }

It always prints that the input is not a number even when integer values are inserted in the textbox. So I'm sure its taking the input as a string input. So do I have to convert it to integer so I can validate? or am I doing something wrong?

An inputs value is **always** of type string, you should be using `isNaN` to check for numeric values. — adeneo, Mar 10 '16 at 21:33
You might be better off using a regular expression to validate your input, depending on what you want to allow. — Dave, Mar 10 '16 at 21:35
Possible duplicate of [Is there a (built-in) way in JavaScript to check if a string is a valid number?](http://stackoverflow.com/questions/175739/is-there-a-built-in-way-in-javascript-to-check-if-a-string-is-a-valid-number) — Heretic Monkey, Mar 10 '16 at 21:52
why not use the html5 `type=number`? The browser will take care of the validation and mobile users should get the correct, numeric, keyboard automatically — Pevara, Mar 11 '16 at 16:02

score 1 · Answer 1 · answered Mar 10 '16 at 21:48

1

You can use parseInt to convert the value to integer, like parseInt("55", 10) will return 55.

And something like parseInt("xx",10) returns NaN.

answered Mar 10 '16 at 21:48

Borys Serebrov

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Enrique Padilla · Answer 2 · 2016-03-11T15:56:49.367

Thanks adeneo, isNaN works for validation.

Code below:

var validate_and_create = function(){
    var i_number = $("input_number").value;
    var isValid = true;

    if (i_number === ""){
        $("create_n_error").firstChild.nodeValue = "Number text field cannot be blank.";
        isValid = false;
    } else {
        if  (isNaN(i_number)) {
            $("create_n_error").firstChild.nodeValue = "This is not a number!";
            isValid = false;
        } else {
            $("create_n_error").firstChild.nodeValue = "This is a number!";
            isValid = true;
        }
    }

How to validate an input as an number in JavaScript

2 Answers2