JavaScript — Check if a String is a Number

In web applications, you can transfer data using the URL. For example, here on Future Studio, we have a listed overview of all published tutorials. This overview is paginated using limit-offset pagination.

Users read through this tutorial list by paginating through the pages using a page query parameter. This page query parameter in the URL is a numeric value and values in the URL are strings. The backend then needs to validate the incoming page parameter and ensure it’s string value is actually a valid number.

This tutorial shows you how to determine whether a given string value is numeric.

Node.js Series Overview

  1. String Replace All Appearances
  2. Remove All Whitespace From a String in JavaScript
  3. Generate a Random ID or String in Node.js or JavaScript
  4. Remove Extra Spaces From a String in JavaScript or Node.js
  5. Remove Numbers From a String in JavaScript or Node.js
  6. Get the Part Before a Character in a String in JavaScript or Node.js
  7. Get the Part After a Character in a String in JavaScript or Node.js
  8. How to Check if a Value is a String in JavaScript or Node.js
  9. Check If a String Includes All Strings in JavaScript/Node.js/TypeScript
  10. Check if a Value is a String in JavaScript and Node.js
  11. Limit and Truncate a String to a Given Length in JavaScript and Node.js
  12. Split a String into a List of Characters in JavaScript and Node.js
  13. How to Generage a UUID in Node.js
  14. Reverse a String in JavaScript or Node.js
  15. Split a String into a List of Lines in JavaScript or Node.js
  16. Split a String into a List of Words in JavaScript or Node.js
  17. Detect if a String is in camelCase Format in Javascript or Node.js
  18. Check If a String Is in Lowercase in JavaScript or Node.js
  19. Check If a String is in Uppercase in JavaScript or Node.js
  20. Get the Part After First Occurrence in a String in JavaScript or Node.js
  21. Get the Part Before First Occurrence in a String in JavaScript or Node.js
  22. Get the Part Before Last Occurrence in a String in JavaScript or Node.js
  23. Get the Part After Last Occurrence in a String in JavaScript or Node.js
  24. How to Count Words in a File
  25. How to Shuffle the Characters of a String in JavaScript or Node.js
  26. Append Characters or Words to a String in JavaScript or Node.js
  27. Check if a String is Empty in JavaScript or Node.js
  28. Ensure a String Ends with a Given Character in JavaScript or Node.js
  29. Left-Trim Characters Off a String in JavaScript or Node.js
  30. Right-Trim Characters Off a String in JavaScript or Node.js
  31. Lowercase the First Character of a String in JavaScript or Node.js
  32. Uppercase the First Character of a String in JavaScript or Node.js
  33. Prepend Characters or Words to a String in JavaScript or Node.js
  34. Check if a String is a Number
  35. Convert a String to Buffer
  36. Prevent Line Breaks in String Template Literals
  37. How to Implement a Custom `toString` Method (Coming soon)
  38. What Is `Symbol.toStringTag` and How to Use It (Coming soon)

Ensure a String is Numeric in JavaScript

Different situations require you to ensure a given input value is a number. If you’re not in control of the input type, you may want to ensure a numeric value is formatted as a string value.

Here’s a utility function allowing you to determine whether a given input is a string or a number in JavaScript:

/**
 * Determine whether the given `input` is a number.
 *
 * @param {String} input
 *
 * @returns {Boolean}
 */
function isNumericString(input) {  
  return typeof input === 'string' && !Number.isNaN(input)
}

The isNumericString utility method ensures the input is a string value. Then it uses JavaScript’s Number.isNaN (“is not a number”) function to determine whether the input is a number.

Enjoy!


Mentioned Resources

Explore the Library

Find interesting tutorials and solutions for your problems.