Check If a String is in Uppercase in JavaScript or Node.js

JavaScript is missing a method to detect whether a given input is a string value in uppercase format. What’s existing are methods allowing us to create our own isUpperCase utility method.

This tutorial shows you how to create a method detecting whether an input is in uppercase.

Node.js Series Overview

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  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 (Coming soon)
  27. Check if a String is Empty in JavaScript or Node.js (Coming soon)
  28. Ensure a String Ends with a Given Character in JavaScript or Node.js (Coming soon)
  29. Left-Trim Characters Off a String in JavaScript or Node.js (Coming soon)
  30. Right-Trim Characters Off a String in JavaScript or Node.js (Coming soon)
  31. Lowercase the First Character of a String in JavaScript or Node.js (Coming soon)
  32. Uppercase the First Character of a String in JavaScript or Node.js (Coming soon)
  33. Prepend Characters or Words to a String in JavaScript or Node.js (Coming soon)
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Determine Whether a JavaScript String is in UPPERCASE

Detecting whether a given input is an uppercase string requires you to create the uppercased version first. Then, you’re comparing the input value against the uppercase version. This check returns true if the values are equal, other false.

JavaScript provides a toUpperCase method on string values. That’s what we’ll use for our isUpperCase method.

You can ensure a string value by wrapping a given input using the globally available String(input) function. This is useful because we can call toUpperCase only on string inputs.

Here’s a sample utility function determining whether a given input is an uppercased string:

/**
 * Determine whether the given `input` is a string in uppercase.
 *
 * @param {*} input
 *
 * @returns {Boolean}
 */
function isUpperCase (input) {  
  return input === String(input).toUpperCase()
}

You may then use the isUpperCase utility function like this:

isUpperCase('FUTURE STUDIO')  
// true

isUpperCase('Future Studio')  
// false

isUpperCase(null)  
// false

isUpperCase()  
// false

Please notice, JavaScript doesn’t treat null or undefined as “nullish” values when using them to create a string. The String() function wraps the given value into a string, like 'null' and 'undefined' (as strings):

String()  
// ''

String(null)  
// 'null'

String(undefined)  
// 'undefined'

This can lead to unexpected behavior in your application when working with nullish values. Depending on your expected behavior you may need to add checks or fallbacks for undefined or null input values to the isUpperCase utility from above.

Use the @supercharge/strings Package

I’m the maintainer of the @supercharge/strings package providing convenient string utilities. It provides a useful Str#isUpper method determining whether a given string is in uppercase:

const Str = require('@supercharge/strings')

Str('FUTURE STUDIO').isUpper()  
// true

Str('Future Studio').isUpper()  
// false

Str(null).isUpper()  
// true

Str().isUpper()  
// true

The @supercharge/strings package treats undefined and null values as empty strings. And empty strings are uppercase by default. That’s the consistent behavior you want in your app 🤝


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