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Posted 16 Jul 2005


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Proper Case JavaScript Function

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16 Jul 2005CPOL2 min read
A one-line code snippet that will turn a string into proper case form (where each letter after a space is capitalized).


I have long searched for a simple code snippet that would let me turn a string into its Capitalized form, known to editors as "proper case". Upon finding nothing, I tried parsing the string one character at a time and switching on the findings; I also tried splitting the string (using spaces as delimiters), altering the first character of each element and gluing the array back into a string (using spaces, Holmes). I was able to locate the characters that needed replacing in an array of either the characters themselves or their positions (indices) within the string, but then some complex code was required to put the whole thing back together.

These attempts worked just fine, but I was still aiming at a simple replace method solution. I finally got it after discovering that JScript 5.5 will take a function as the replaceText argument.


First, let us refresh our knowledge on regular expressions. We must locate each character after a space and remember such locations. Fortunately, the regular expression object does capture 9 "submatches" or occurrences in a set of properties. The regular expression syntax for capturing any single character after a space follows:


I rather use the space specifier \s than an actual blank in the code to improve readability and to include any form-feed, tabs, etc. in the match.

The first character of the string must be capitalized too, so we'll use the input beginning specifier and capture whatever character is exactly after it:


Our lookup expression then combines into:


Now, the use of the $n properties in the replacement text has limitations I am not going to elaborate about; in this particular case, the beauty of using a function relies on three facts:

  1. The $1 regular expression property can be used as a function argument;
  2. The $1 regular expression property can be used inside the function, and
  3. The $1 regular expression property is updated internally by the replace method after the function executes!

Because of this, the $1 property always represents the next submatch. All that is left to do is to turn the entire string into lower case and each match to upper case using our replace function:

// proper case function (JScript 5.5+)
function toProperCase(s)
  return s.toLowerCase().replace(/^(.)|\s(.)/g, 
          function($1) { return $1.toUpperCase(); });

Alternatively, if you prefer, in prototype flavor:

// proper case string prptotype (JScript 5.5+)
String.prototype.toProperCase = function()
  return this.toLowerCase().replace(/^(.)|\s(.)/g, 
      function($1) { return $1.toUpperCase(); });

Bear in mind that this is no thesaurus, its primary use is for proper names, i.e. turning HECTOR J. RIVAS or hector j. rivas into Hector J. Rivas... You will need a second pass function of your device to skip articles or other words in phrases, say to turn the opening sentence in this paragraph into: Bear in Mind that this is no Thesaurus.

I sure would like to know the internals of the replace function, the regular expression object and the function as replace text, since I mostly use it in database apps, but so far, it reports better speed and efficiency than any other method I have tried.

Hope you like it.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

hector [.j.] rivas
Software Developer (Senior) Texas Capital Bank
United States United States
Professional software engineer with 30+ years of experience delivering systems across diverse industries, looking for the next opportunity to deliver cutting edge end-to-end technology solutions.

Avid reader, disciplined writer and enthusiastic tinkerer with a background in electronics, looking inside and thinking outside the box, genuinely passionate about robust, extensible, reusable and performant code.

Framework developer leading, coaching and learning about best practices, code quality, DevOps and software and data lifecycle management with an agile mindset to create the most elegant and sustainable solutions.

Comments and Discussions

QuestionHypehn names Pin
Member 1490370531-Jul-20 0:38
MemberMember 1490370531-Jul-20 0:38 
Great snippet, but I think you should also handle hyphenated names, like Mary-Jane Lastname.
I'm using this expression to also handle this case:

QuestionWhy the function? Pin
Christopher Lord16-Jul-05 11:17
MemberChristopher Lord16-Jul-05 11:17 
AnswerRe: Why the function? Pin
hector [.j.] rivas16-Jul-05 11:57
Memberhector [.j.] rivas16-Jul-05 11:57 
GeneralRe: Why the function? Pin
Christopher Lord16-Jul-05 18:13
MemberChristopher Lord16-Jul-05 18:13 
GeneralRe: Why the function? Pin
hector [.j.] rivas18-Jul-05 14:32
Memberhector [.j.] rivas18-Jul-05 14:32 
GeneralRe: Why the function? Pin
Lwangaman3-Feb-10 6:36
MemberLwangaman3-Feb-10 6:36 
AnswerRe: Why the function? Pin
hector [.j.] rivas3-Feb-10 7:08
Memberhector [.j.] rivas3-Feb-10 7:08 
GeneralRe: Why the function? Pin
Lwangaman3-Feb-10 11:15
MemberLwangaman3-Feb-10 11:15 
GeneralRe: Why the function? Pin
tdmeers8-Nov-10 9:44
Membertdmeers8-Nov-10 9:44 

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