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

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.

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  1. String Replace All Appearances
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  6. Get the Part Before a Character in a String 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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  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
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  14. Reverse a String in JavaScript or Node.js
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  17. Detect if a String is in camelCase Format in Javascript or Node.js
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  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
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  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
  38. What Is `Symbol.toStringTag` and How to Use It (Coming soon)
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  6. Sort an Array of Integers in JavaScript and Node.js
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  6. Detect if Value Is a Promise in Node.js and JavaScript
  7. Overview of Promise-Based APIs in Node.js
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  2. Write a JSON Object to a File
  3. Create a Custom “toJSON” Function in Node.js and JavaScript
  4. Securely Parse JSON
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  5. Use Numeric Separators for Better Readability
  6. Convert Boolean to Number
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  8. Check if a Value is a Number
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  2. How to Check if an Object is Empty in JavaScript or Node.js
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  7. How to Delete a Key From an Object in JavaScript or Node.js
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  9. How to Convert URLSearchParams to Object
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  11. Conditionally Add Properties to an Object in JavaScript or Node.js
  12. How to Lowercase Keys of an Object in JavaScript or Node.js
  13. Unset an Object Property
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  3. How to Create an Empty File
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  6. Check If a Path Is a Directory
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  9. How to Touch a File
  10. Read File Content as String
  11. Check If a Directory Is Empty
  12. How to Create a Directory (and Parents If Needed)
  13. Get a File‘s Extension
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  16. Read a JSON File
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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

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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