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Lowercase the First Character of a String in JavaScript or Node.js

When working with strings you may want to transform the first character of a given value. This could happen when you scaffold files for a project and want to ensure a given function name starts with a lowercase character.

Or you’re doing something else and still want to know how to lowercase the first character of a string using JavaScript. Then, please read on.

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Lowercase the First Letter of a String in JavaScript

Lowercasing the first character comes with some checks before changing the casing of a string.

First, you must ensure a given value is a string. You can use the typeof operator for that check. We also have a dedicated tutorial on checking whether a value is a string which could be of interest to you.

Second, you can only lowercase the first character in a string if its value isn’t empty. In case of an empty string you want to return an empty string as well.

Third, process the lowercasing using JavaScript’s String#toLowerCase method.

Here’s a lcFirst utility method accepting a string as an argument and returning the string with a lowercased first character:

/**
 * Lowercases the first character in the `string`.
 *
 * @param {String} string
 *
 * @returns {String}
 */
function lcFirst (string) {  
  if (typeof string !== 'string') { 
    return ''
  }

  if (string.length === 0) {
    return string
  }

  return string[0].toLowerCase() + string.slice(1)
}

Now you can use the created lcFirst function like this:

lcFirst()  
// ''

lcFirst('')  
// ''

lcFirst('A')  
// 'a'

lcFirst('ABC')  
// 'aBC'

lcFirst('UserModel')  
// 'userModel'

lcFirst('Future Studio')  
// 'future Studio'

Use the @supercharge/strings Package

I’m the maintainer of the @supercharge/strings package, which provides convenient string utilities. The @supercharge/strings package comes with a handy Str#lcFirst method.

This lcFirst method lowercases the first character in a string and leaves the rest “as is”:

import { Str } from '@supercharge/string'

Str().lcFirst().get()  
// ''

Str('').lcFirst().get()  
// ''

Str('A').lcFirst().get()  
// 'a'

Str('ABC').lcFirst().get()  
// 'aBC'

Str('UserModel').lcFirst().get()  
// 'userModel'

Str('Future Studio').lcFirst().get()  
// 'future Studio'

Enjoy lowercasing the first character of a string!

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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