Regex to split camel case

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'))

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')

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

outputs:

"My Camel Case String"

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'));