Regex to split camel case

Question

I have a regular expression in JavaScript to split my camel case string at the upper-case letters using the following code (which I subsequently got from here):

"MyCamelCaseString"
    .replace(/([A-Z])/g, ' $1')
    .replace(/^./, function(str){ return str.toUpperCase(); })

Thus that returns:

"My Camel Case String"

Which is good. However, I want to step this up a notch. Could someone help me with a regex which will split if, and only if, the former character is lower-case and the latter is upper-case.

Thus, the above example will be the result I expect, but if I do:

"ExampleID"

Then I get returned:

"Example ID"

Instead of

"Example I D"

Since it's splitting at each upper-case and ignoring anything before it.

Hope that makes sense! And thanks :).

Answer 1

My guess is replacing /([A-Z])/ with /([a-z])([A-Z])/ and ' $1' with '$1 $2'

"MyCamelCaseString"
    .replace(/([a-z])([A-Z])/g, '$1 $2');

/([a-z0-9])([A-Z])/ for numbers counting as lowercase characters

console.log("MyCamelCaseStringID".replace(/([a-z0-9])([A-Z])/g, '$1 $2'))

Answer 2

"MyCamelCaseString".replace(/([a-z](?=[A-Z]))/g, '$1 ')

outputs:

"My Camel Case String"

Answer 3

If you want an array of lower case words:

"myCamelCaseString".split(/(?=[A-Z])/).map(s => s.toLowerCase());

If you want a string of lower case words:

"myCamelCaseString".split(/(?=[A-Z])/).map(s => s.toLowerCase()).join(' ');

If you want to separate the words but keep the casing:

"myCamelCaseString".replace(/([a-z])([A-Z])/g, '$1 $2')

Answer 4

Sometime camelCase strings include abbreviations, for example:

PDFSplitAndMergeSamples
PDFExtractorSDKSamples
PDFRendererSDKSamples
BarcodeReaderSDKSamples

And in this case the following function will work, it splits the string leaving abbreviations as separate strings:

function SplitCamelCaseWithAbbreviations(s){
   return s.split(/([A-Z][a-z]+)/).filter(function(e){return e});
}

Example:

function SplitCamelCaseWithAbbreviations(s){
   return s.split(/([A-Z][a-z]+)/).filter(function(e){return e});
}

console.log(SplitCamelCaseWithAbbreviations('PDFSplitAndMergeSamples'));
console.log(SplitCamelCaseWithAbbreviations('PDFExtractorSDKSamples'));
console.log(SplitCamelCaseWithAbbreviations('PDFRendererSDKSamples'));
console.log(SplitCamelCaseWithAbbreviations('BarcodeReaderSDKSamples'));

Answer 5

I found that none of the answers for this question really worked in all cases and also not at all for unicode strings, so here's one that does everything, including dash and underscore notation splitting.

let samples = [
  "ThereIsWay_too  MuchCGIInFilms These-days",
  "UnicodeCanBeCAPITALISEDTooYouKnow",
  "CAPITALLetters at the StartOfAString_work_too",
  "As_they_DoAtTheEND",
  "BitteWerfenSie-dieFußballeInDenMüll",
  "IchHabeUberGesagtNichtÜber",
  "2BeOrNot2Be",
  "ICannotBelieveThe100GotRenewed. It-isSOOOOOOBad"
];

samples.forEach(sample => console.log(sample.replace(/([^[\p{L}\d]+|(?<=[\p{Ll}\d])(?=\p{Lu})|(?<=\p{Lu})(?=\p{Lu}[\p{Ll}\d])|(?<=[\p{L}\d])(?=\p{Lu}[\p{Ll}\d]))/gu, '-').toUpperCase()));

If you don't want numbers treated as lower case letters, then:

let samples = [
  "2beOrNot2Be",
  "ICannotBelieveThe100GotRenewed. It-isSOOOOOOBad"
];

samples.forEach(sample => console.log(sample.replace(/([^\p{L}\d]+|(?<=\p{L})(?=\d)|(?<=\d)(?=\p{L})|(?<=[\p{Ll}\d])(?=\p{Lu})|(?<=\p{Lu})(?=\p{Lu}\p{Ll})|(?<=[\p{L}\d])(?=\p{Lu}\p{Ll}))/gu, '-').toUpperCase()));

Answer 6

If you want to capitalize and add space between numbers as well, this works.

transform(value: string, ...args: any[]): string {
    const str = 'this1IsASampleText';
    str.charAt(0).toUpperCase() + value.slice(1); // Capitalize the first letter
    str.replace(/([0-9A-Z])/g, ' $&'); // Add space between camel casing
}

Results:

This 1 Is A Sample Text    

Answer 7

Hi I saw no live demo , thanks @michiel-dral

var tests =[ "camelCase",
             "simple",
             "number1Case2",
             "CamelCaseXYZ",
             "CamelCaseXYZa" 
           ]

function getCamelCaseArray(camel) {
  var reg = /([a-z0-9])([A-Z])/g;
  return camel.replace(reg, '$1 $2').split(' ');
}

function printTest(test) {
document.write('<p>'+test + '=' + getCamelCaseArray(test)+'</p>');
}

tests.forEach(printTest);

<!DOCTYPE html>
<html>

  <head>
    <link rel="stylesheet" href="style.css">
    <script src="script.js"></script>
  </head>

  <body>
  </body>

</html>

Answer 8

Regex not-a word boundary \B character can also be used

console.log("MyCamelCaseString".replace(/(\B[A-Z])/g, ' $1'));

Answer 9

a = 'threeBlindMice'
a.match(/[A-Z]?[a-z]+/g) // [ 'three', 'Blind', 'Mice' ]

is the simplest way I've found, for simple camel/titlecase splitting.

Answer 10

If you're like me and had a camelCase value such as:

thisIsMyCamelCaseValue where the first letter is lowercased

function fromCamelCase(value) {
    const spaced = value.replace(/([a-z])([A-Z])/g, '$1 $2');
    return spaced.charAt(0).toUpperCase() + spaced.slice(1);
}

Answer 11

I prefer to work with arrays over strings. It's easier to debug and more flexible. This is an actual join instead of replace. I haven't dealt with white spaces in the strings but you could just trim each element easily enough.

const splitCamelCase = str => str.match(/^[A-Z]?[^A-Z]*|[A-Z][^A-Z]*/g).join(' ');

console.log(splitCamelCase('fooMyCamelCaseString'));
console.log(splitCamelCase('MyCamelCaseString'));
console.log(splitCamelCase('XYZMyCamelCaseString'));
console.log(splitCamelCase('alllowercase'));

Answer 12

You can use a combination of regEx, replace, and trim.

"ABCMyCamelCaseSTR".replace(/([A-Z][a-z0-9]+)/g, ' $1 ')
                   .replace(/\s{2}/g," ").trim()

// ABC My Camel Case STR

Answer 13

I recently came across this question and needed to do the exact same thing:

employeeID should be rendered as Employee ID

I found this convert case library from zellwk plus a little additional reduce function did the trick for me:

import { toTitle } from "./convert-case.js";

// NB. Assumes sequential single chars can be concatenated
// ex. N B A Finals => NBA Finals
const reducer = (total, currentValue, currentIndex, arr) => {
  if (
    currentValue.length === 1 &&
    !(currentIndex > 0 && arr[currentIndex - 1].length > 1)
  ) {
    return total + currentValue;
  } else {
    return total + " " + currentValue;
  }
};

const concatSingleChars = (title) => {
  const arrTitle = title.split(" ");
  return arrTitle.reduce(reducer);
};

const convertCase = (str) => {
  const s = toTitle(str);
  return concatSingleChars(s);
};

const tests = [
  "colName",
  "This_Is_A_title",
  "And_How_About_thisOne",
  "MaryHadALittleLamb",
  "employeeID",
  "N B A Finals",
  "N B A Finals in L A",
  "I Love L A"
];

const titles = tests.map((test) => {
  return convertCase(test);
});

console.log(titles);

Answer 14

Here is what I got from Github Copilot — the explanation is mine, this is not fully AI generated —:

1. Put a space in front a capital letters via the /([A-Z])/g regex.
2. Capitalize whatever is at the beginning of the string via the /^./ regex.
3. Trim the leading and trailing white space with the .trim() method.

Here is the final code:

function camelCaseToCapitalized(str: string) {
  return str
    .replace(/([A-Z])/g, " $1")
    .replace(/^./, (str) => str.toUpperCase())
    .trim();
}

Answer 15

This RegExp String is

.replace("/([a-zA-Z][a-z]*)/g",...);