Javascript Number

JavaScript: is number

Written by: Ryan Frankel

Ryan Frankel

Ryan began developing websites in the late '90s and has personally tested just about every web host and cloud platform worth trying on the market today. With a masters degree in electrical and computer engineering from the University of Florida, he leverages his extensive knowledge of hardware, software, and their engineering relationship to inform HostingAdvice readers of the technical implications of their hosting choices. Ryan's subject matter expertise includes, but is not limited to, WordPress, cloud infrastructure management, product UI/UX design, and popular web development languages such as JavaScript and PHP.

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Edited by: Lillian Castro

Lillian Castro

Lillian brings more than 30 years of editing and journalism experience to our team. She has written and edited for major news organizations, including The Atlanta Journal-Constitution and the New York Times, and she previously served as an adjunct instructor at the University of Florida. Today, she edits HostingAdvice content for clarity, accuracy, and reader engagement.

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Deciding whether something is a number in JavaScript should be a straightforward type check (i.e., using the isNaN() function), but, as it turns out, it is a bit more tricky.

How to Determine Whether or Not Something is a Number in JavaScript

This is due to JavaScript’s forced conversion-to-number behavior. The often used methods, isNaN() and isFinite() can have confusing behavior and return incorrect answers.

Thankfully, ECMAScript 6 (JS language specification) was released with the intention of fixing these issues with Number.isNaN() and Number.isFinite(), along with making many other language clarifications and improvements.

Use the isNumeric() Function

Until that JS language version is the standard and used in browsers, we will need to be careful when checking if a value is a number.

The jQuery project has a tiny isNumeric() function implementation that fixes this odd JS behavior. There are some other implementations, but many of those fail in some of the JS type-casting-gotcha corner cases.

The isNumeric() function below is usable in your own code, even without jQuery.

var isNumeric = function(obj){    return !Array.isArray( obj ) && (obj - parseFloat( obj ) + 1) >= 0;  }

isNumeric() Examples

Below are some examples of using isNumeric() with its boolean output:

isNumeric(10); // true  isNumeric(“0.75”); // true  isNumeric(“123e–2”); // true  isNumeric(–0xFFF); // true    isNumeric(Infinity); // false , use isFinite()  isNumeric(NaN); // false , use isNaN()  isNumeric([1]); // false  isNumeric(true); // false  isNumeric(“foo”); // false  isNumeric(null); // false  isNumeric(new Date()); // false
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ABOUT THE AUTHOR

Ryan Frankel has been a professional in the tech industry for more than 20 years and has been developing websites for more than 25. With a master's degree in electrical and computer engineering from the University of Florida, he has a fundamental understanding of hardware systems and the software that runs them. Ryan now sits as the CTO of Digital Brands Inc. and manages all of the server infrastructure of their websites, as well as their development team. In addition, Ryan has a passion for guitars, good coffee, and puppies.

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