Case Conversion in JavaScript

Published:Dec 30, 2020

I got fed-up searching Google for case conversion utilities. The useful ones I found (Voca and change-case) both require an environment that allows me to use npm.

But I was using Vanilla JavaScript. I did not want to include any toolchains in this project, and I’m reluctant to send an asynchronous request to download a module just for case-conversion.

So I decided to write a set of conversion utilities myself.

It’s simpler than I thought.

The Common Cases

I usually use these cases when writing HTML, CSS, and JavaScript:

camelCase
kebab-case
Sentence case
Title Case

I don’t use these two cases, but I know they exist.

snake_case
PascalCase

So far, I’ve relied on simple functions that convert from one case to another. But I was fed-up with writing things like camelToTitle or camelToKebab. It’s much nicer to have a function that converts all cases to the one I need.

Converting any case to kebab-case

I started converting stuff into kebab-case because that was what I needed when I searched for case conversion utilities.

To convert all cases into kebab-case, I had to consider the possible cases. Here are the cases once again:

camelCase
PascalCase
snake_case
Sentence case
Title Case

Converting snake_case, Sentence case and Title Case into kebab-case is easy. I only need to do two things:

Lowercase everything
Replace _ and spaces with -

But I cannot begin by lowercasing everything if I want to support case conversion from camelCase and PascalCase. I would lose the word-break point.

So I had to begin by searching for the capital letters which denote the start of a new word (for camelCase and PascalCase). The easiest way is to loop through each letter and run a simple /[A-Z]/ regex. This regex searches for any letter that’s between A and Z.

function toKebab(string) {
  return string
    .split('')
    .map((letter, index) => {
      if (/[A-Z]/.test(letter)) {
        // Capital letters
      }
      return letter
    })
    .join('')
}

Then I lowercased the capital letters and added a space in front of them. (It doesn’t matter whether I add space or _, both are fine since I’m going to replace them with - later).

function toKebab(string) {
  return string
    .split('')
    .map((letter, index) => {
      if (/[A-Z]/.test(letter)) {
        return ` ${letter.toLowerCase()}`
      }
      return letter
    })
    .join('')
}

Note: I’m pretty sure there’s a regex that can do these three steps in one. It probably uses capturing groups and substitution, which I’m not familiar with. I didn’t try it since I didn’t have the time nor energy to research further. If you know a good regex for this, let me know!

This step converts the cases into the following:

camel case
pascal case
snake_case
sentence case
title case

There’s a space at the start of some cases. I removed them with trim.

function toKebab(string) {
  return string
    .split('')
    .map((letter, index) => {
      if (/[A-Z]/.test(letter)) {
        return ` ${letter.toLowerCase()}`
      }
      return letter
    })
    .join('')
    .trim()
}

This gives me the following:

camel case
pascal case
snake_case
sentence case
title case

I can now replace both _ and spaces with -. This can be done with two replace calls like this:

1. First, replace uses /_/g to replace all occurrences of _.
1. Second, replace uses /\s+/ to replace all spaces into -. The + indicates “one or more”, so it matches the two spaces in title case.

export function toKebab(string) {
  return (
    string
      // ...
      .replace(/_/g, '-')
      .replace(/\s+/g, '-')
  )
}

I can combine both replace calls into a single regex with []. The square brackets indicate an OR value.

export function toKebab(string) {
  return (
    string
      // ...
      .replace(/[_\s]+/g, '-')
  )
}

That gives me this:

camel-case
pascal-case
snake-case
sentence-case
title-case

It even works for complicated mixed cases too. For example, if you try case_With-long name you’ll get case-with-long-name.

Converting anything to Sentence case

I worked on this utility next since I wanted to convert camelCase into Sentence case.

At first, I dreaded the thought of finding the similarities between all 6 cases again. It felt like a lot of work.

But I realized I can use my toKebab function to convert everything into kebab-case first. This takes advantage of the work I’ve already done.

I was against this idea at first because from a performance standpoint, it seemed like a “waste of resources” to run another function first. But I realized I was being idealistic. From a practical standpoint, it doesn’t have much impact on performance since the operations are really fast.

// Starting with toKebab
function toTitle(string) {
  return toKebab(string)
}

Now I just need to convert kebab-case to Title Case.

Here, I only need to do the following:

Split the string at -. This gives me an array of words.
Capitalize the first letter of each word.
Join the array with space.

export function toTitle(string) {
  return toKebab(string)
    .split('-')
    .map(word => {
      return word.slice(0, 1).toUpperCase() + word.slice(1)
    })
    .join(' ')
}

And I’m done!

Converting anything into Sentence case

It’s equally easy to convert all cases into Sentence case. Once again, I started by converting things into kebab-case.

export function toSentence(string) {
  return toKebab(string)
}

Now I only need to convert kebab-case into Sentence case. There are two things to do:

Capitalize the first letter
replace - with space.

I can do either step first. In this case, I chose to do the replace step first since I can chain it after toKebab.

export function toSentence(string) {
  const interim = toKebab(string).replace(/-/g, ' ')
  return interim.slice(0, 1).toUpperCase() + interim.slice(1)
}

Convert anything into camelCase

Finally, I want to be able to convert any string back into camel case.

I start with toKebab as usual.

export function toCamel(string) {
  return toKebab(string)
}

At this point, I only need to convert kebab-case into camelCase.

I can do this by:

Splitting the word at each -. This creates an array of words.
Loop through the array and capitalize the first letter, if it’s not the first word.

function toCamel(string) {
  return toKebab(string)
    .split('-')
    .map((word, index) => {
      if (index === 0) return word
      return word.slice(0, 1).toUpperCase() + word.slice(1).toLowerCase()
    })
    .join('')
}

Simple as that!

Case Conversion Library

I placed added these case-conversion utilities into my JavaScript repository. You can grab them if you want them :)