Code of the Day: Javascript, Fix for isNaN

Javascript is a dynamically typed langauges. This feature causes for Arrays, Booleans, and other types to be converted to a numeric values depending on usage.
However this feature can cause headarches when trying to detect numbers.

For example, isNaN() detects if a value is a non-number. That’s what NaN stands for, “Not a number”.
So you might think that the opposite result from isNaN() would indicate if a value is a number.

// Works for most cases but not for strict comparisons.
var isNumber = function(val){
	return !isNaN( val );

Note: Click the “result” tab to run the test cases in

So here’s a simple fix for isNaN and isNumber.

// isNaN2 returns a boolean for if a value is not a number or +-Infinity
var isNaN2 = (function (global) {
    var _isNaN = global.isNaN;
    return function (val) {
        return _isNaN("" + val) || (typeof val === "object" && !(val || "").hasOwnProperty('push'));
// isNumeric returns a boolean for if a value is a number or +-Infinity
var isNumeric = (function (global) {
    var _isNaN = global.isNaN;
    return function (val) {
        return !_isNaN("" + val)&&(typeof val !== "object" || (val || "").hasOwnProperty('push'));

isNaN vs isNaN2

Testcases for isNaN2 and isNumeric

Well it turns out that jQuery has a better implementation. The only difference is that infinity is not a number, which is correct.

$.isNumeric = function( obj ){
    return !isNaN( parseFloat( obj ) ) && isFinite( obj );

Larry Battle

I love to program, and discover new tech. Check out my stackoverflow and github accounts.

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