How to Titleize a Sentence in JavaScript

We recently ran into a scenario at work where we went through the process to redo all the email templates used in our application. There were over 300+ templates that we redesigned. After we finished somebody requested that we change the subject line to be title cased like you would in a print headline. Not wanting to manually change all 300+ templates, I wrote this quick function that handled the process automatically.

What is Title Case

At first glance it might sound like we wanted the first letter of every word in a the subject line to be uppercase and the remainder of the word to be lowercase.

Well that is almost correct. We don't want certain words to be capitalized. Words like a, an or and we wanted to remain lowercase.

Here is the quick function I created that handled this transition for us.

First I created an array of words that we wanted to remain lowercase in the subject of the email.

const small_words = ['a', 'an', 'and', 'as', 'at', 'but', 'by', 'for', 'if', 'in', 'into', 'nor', 'of', 'on', 'or', 'out', 'so', 'the', 'to', 'up', 'yet', 'and', 'as', 'at', 'but', 'by', 'for', 'if', 'in', 'into', 'nor', 'of', 'on', 'or', 'out', 'so', 'the', 'to', 'up', 'yet'];

Next I created a function that would have the text of the subject line passed into it. I would break this string into an array with each word in the subject an entry in the array. Now that I have an array I can loop over every word. If the word matches an entry in the small_words array then I convert it to lowercase. Otherwise I capitalize the first letter of the word and lowercase the remainder of the word.

There is one exception that I have to account for and that is the first letter in the subject text. Regardless of what is the first word I want it to have the first letter capitalized.

With those requirements, here is my function:

const titleize = (title) => {
  return title.split(' ').map((word, index) => {
    if (index !== 0 && small_words.includes(word)) {
      return word.toLowerCase();
    } else {
      return word[0].toUpperCase() + word.slice(1).toLowerCase();
    }
  }).join(' ');
}

To test out the function I added 3 titles and console.log the new title.

console.log(titleize('notes on a scandal'));  // Notes on a Scandal
console.log(titleize('a good man is hard to find')); // A Good Man Is Hard to Find
console.log(titleize('midnight in the garden of good and evil')); // Midnight in the Garden of Good and Evil

You will see the output for each test of a subject line.

If you ever need to titleize a string based on print title formatting, you can use this function. All you would need to do is edit the small_words array to include your list of words to remain lowercase.