Convert Camel Case To Sentence Case In Javascript

I found myself needing to do camel case to sentence case string conversion with sane acronym support, a google search for ideas led me to the following SO post: Convert camelCaseTe

Solution 1:

The below uses capitalised notation for acronyms; I don't agree with Microsoft's recommendation of capitalising when more than two characters so this expects the whole acronym to be capitalised even if it's at the start of the string (which technically means it's not camel case but it gives sane controllable output), multiple consecutive acronyms can be escaped with _ (e.g. parseDBM_MXL -> Parse DBM XML).

function camelToSentenceCase(str) {
    return str.split(/([A-Z]|\d)/).map((v, i, arr) => {
        // If first block then capitalise 1st letter regardless
        if (!i) return v.charAt(0).toUpperCase() + v.slice(1);
        // Skip empty blocks
        if (!v) return v;
        // Underscore substitution
        if (v === '_') return " ";
        // We have a capital or number
        if (v.length === 1 && v === v.toUpperCase()) {
            const previousCapital = !arr[i-1] || arr[i-1] === '_';
            const nextWord = i+1 < arr.length && arr[i+1] && arr[i+1] !== '_';
            const nextTwoCapitalsOrEndOfString = i+3 > arr.length || !arr[i+1] && !arr[i+3];
            // Insert space
            if (!previousCapital || nextWord) v = " " + v;
            // Start of word or single letter word
            if (nextWord || (!previousCapital && !nextTwoCapitalsOrEndOfString)) v = v.toLowerCase();
        }
        return v;
    }).join("");
}


// ----------------------------------------------------- //

var testSet = [
    'camelCase',
    'camelTOPCase',
    'aP2PConnection',
    'JSONIsGreat',
    'thisIsALoadOfJSON',
    'parseDBM_XML',
    'superSimpleExample',
    'aGoodIPAddress'
];

testSet.forEach(function(item) {
    console.log(item, '->', camelToSentenceCase(item));
});