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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.

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  8. Check if a Value Is Null or Undefined in JavaScript or Node.js
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  8. How to Check if a Value is a String in JavaScript or Node.js
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  20. Get the Part After First Occurrence in a String in JavaScript or Node.js
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  22. Get the Part Before Last Occurrence in a String in JavaScript or Node.js
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  27. Check if a String is Empty in JavaScript or Node.js
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  34. Check if a String is a Number
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  5. Use Numeric Separators for Better Readability
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  8. Check if a Value is a Number
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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

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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