Convert camelCaseText to Sentence Case Text

Question

How can I convert a string either like \'helloThere\' or \'HelloThere\' to \'Hello There\' in JavaScript?

Answer 1

One more solution based on RegEx.

respace(str) {
  const regex = /([A-Z])(?=[A-Z][a-z])|([a-z])(?=[A-Z])/g;
  return str.replace(regex, '$& ');
}

Explanation

The above RegEx consist of two similar parts separated by OR operator. The first half:

1. ([A-Z]) - matches uppercase letters...
2. (?=[A-Z][a-z]) - followed by a sequence of uppercase and lowercase letters.

When applied to sequence FOo, this effectively matches its F letter.

Or the second scenario:

1. ([a-z]) - matches lowercase letters...
2. (?=[A-Z]) - followed by an uppercase letter.

When applied to sequence barFoo, this effectively matches its r letter.

When all replace candidates were found, the last thing to do is to replace them with the same letter but with an additional space character. For this we can use '$& ' as a replacement, and it will resolve to a matched substring followed by a space character.

Example

const regex = /([A-Z])(?=[A-Z][a-z])|([a-z])(?=[A-Z])/g
const testWords = ['ACoolExample', 'fooBar', 'INAndOUT', 'QWERTY', 'fooBBar']

testWords.map(w => w.replace(regex, '$& '))
->(5) ["A Cool Example", "foo Bar", "IN And OUT", "QWERTY", "foo B Bar"]