convertCase.js

function convertCase(s, toDelim) {
    if (!s || !s.length) return s

    var existingType, lastFoundDelim = -1, camelCaseIndex = {}
    if(s.indexOf(' ') > -1) existingType = ' ';
    if(s.indexOf('-') > -1) existingType = '-';
    if(s.indexOf('_') > -1) existingType = '_';
    if(s.indexOf('.') > -1) existingType = '.';
    if(!existingType) {
        for(var i = 0; i < s.length; i++) {
            var v = s[i]
            var currentType = ''

            
            if (lastFoundDelim == i - 1 && v == v.toUpperCase()) {
                lastFoundDelim = i
                currentType = 'camel'
                camelCaseIndex[i] = true
            } else if (lastFoundDelim == i - 1 && v == v.toLowerCase()) {
                lastFoundDelim = i
                currentType = 'camel'
            }

            if(!currentType) continue
            if(!existingType || currentType == existingType) {
                existingType = currentType
            }
        }
    }

    function toType() {
        if(existingType == toDelim) return s
        if(!toDelim || toDelim == 'camel') {
            return toCamel()
        }
        if(!toDelim || toDelim == 'uc') {
            return toUpperCamel()
        }
        switch (existingType) {
            case ' ':
            case '_':
            case '-':
            case '.':
                return fromDelim()
                break
            case 'camel':
                return fromCamel()
                break
            default:
                return s
        }
    }

    function replaceAll(str, find, replace) {
        return str.replace(new RegExp(find, 'g'), replace);
    }

    function fromDelim() {
        return replaceAll(s, existingType, toDelim)
    }

    function fromCamel() {
        var newS = '', lastLowerCase = -1, lastUpperCase = -1, lastDelim = -1
        for(var i = 0; i < s.length; i++) {
            const v = s[i]
            if(camelCaseIndex[i]) {
                newS += toDelim + v.toLowerCase()
            } else {
                newS += v.toLowerCase()
            }
        }
        return newS
    }

    function toCamel() {
        var newS = '', lastLowerCase = -1, lastUpperCase = -1
        var lastFoundDelim = -1
        for(var i = 0; i < s.length; i++) {
            const v = s[i]
            if (v == existingType) {
                lastFoundDelim = i
            } else if (lastFoundDelim == i - 1 && v == v.toUpperCase() && i > 0) {
                lastUpperCase = i
                newS += v.toLowerCase()
            } else if (lastFoundDelim == i - 1 && v == v.toLowerCase() && i > 0) {
                lastLowerCase = i
                newS += v.toUpperCase()
            } else {
                newS += v
            }
        }
        return newS
    }

    function toUpperCamel() {
        var newS = ''
        var lastFoundDelim = -1
        for(var i = 0; i < s.length; i++) {
            const v = s[i]
            if (v == existingType) {
                lastFoundDelim = i
            } else if (lastFoundDelim == i - 1 && v == v.toUpperCase()) {
                lastUpperCase = i
                newS += v.toLowerCase()
            } else if (lastFoundDelim == i - 1 && v == v.toLowerCase()) {
                lastLowerCase = i
                newS += v.toUpperCase()
            } else {
                newS += v
            }
        }
        return newS
    }
  return  toType()
}

console.log(convertCase('weAreHereToHelp', '.'))
//console.log(convertCase('we_are_here_to_help'))
//console.log(convertCase('we_are_here_to_help', 'uc'))