Check if a Value is a String in JavaScript and Node.js

Sometimes you want to ensure a given value is actually a string. For example, you may want to confirm a name property to be a string value.

This tutorial shows you how to detect whether a given value is a string in JavaScript.

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 (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)
  1. Get Number of Seconds Since Epoch in JavaScript
  2. Get Tomorrow’s Date in JavaScript
  3. Increase a Date in JavaScript by One Week
  4. Add Seconds to a Date in Node.js and JavaScript
  5. Add Month(s) to a Date in JavaScript or Node.js
  6. Add Week(s) to a Date in JavaScript or Node.js
  7. Get the Current Year in JavaScript or Node.js
  8. How to Get a UNIX Timestamp in JavaScript or Node.js
  9. How to Convert a UNIX Timestamp to a Date in JavaScript or Node.js
  10. Add Days to a Date in JavaScript or Node.js
  11. Get Yesterday's Date in JavaScript or Node.js
  12. Add Minutes to a Date in JavaScript or Node.js (Coming soon)
  13. Add Hours to a Date in JavaScript or Node.js (Coming soon)
  14. Check If a Date Is Today in JavaScript or Node.js (Coming soon)
  15. Check If a Date is Tomorrow in JavaScript or Node.js (Coming soon)
  16. Check If a Date is Yesterday in JavaScript or Node.js (Coming soon)
  17. How to Format a Date YYYY-MM-DD in JavaScript or Node.js (Coming soon)

Determine If a Given Value Is a JavaScript String

JavaScript has the typeof operator. It returns the underlying type of a variable. This operator is useful when determining whether a given input value is a string:

/**
 * Determine whether the given `input` is a string.
 *
 * @param {*} input
 *
 * @returns {Boolean}
 */
function isString (input) {  
  return typeof input === 'string' && Object.prototype.toString.call(input) === '[object String]'
}

isString('Hello Marcus')  
// true

isString(123)  
// false

I guess in 99% of all cases you’re totally fine just using the typeof input === 'string' check.

Well, you may ask “why doing the extra Object.prototype.toString.call(input)call” then? You know, shit can go crazy in JavaScript! Sometimes you’re tinkering with prototypes of an instance or assigning a new value to the constructor property. This extra toString comparison is the layer ensuring you’re catching the 1% cases.

Use the @supercharge/strings Package

I’m the maintainer of the @supercharge/strings package providing convenient string utilities. It provides a convenient Str.isString(value) method determining whether a given value is a string:

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

const isString = Str.isString('Hello')  
// true

Str.isString(null) // false  
Str.isString(1234) // false  
Str.isString([1, 2, 3]) // false  
// … and so on :)

Enjoy!


Mentioned Resources

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