Implementation of converting between underline and camel case in js (multiple methods)

function toLowerLine(str) {
 var temp = str.replace(/[AZ]/g, function (match) { 
  return "_" + match.toLowerCase();
   });
   if(temp.slice(0,1) === '_'){ //If the first letter is uppercase, there will be an extra _ when executing replace, so you need to remove it here temp = temp.slice(1);
   }
 return temp;
};
console.log(toLowerLine("TestToLowerLine")); //test_to_lower_line
console.log(toLowerLine("testToLowerLine")); //test_to_lower_line

function toCamel(str) {
   return str.replace(/([^_])(?:_+([^_]))/g, function ($0, $1, $2) {
     return $1 + $2.toUpperCase();
   });
}
console.log(toCamel('test_to_camel')); //testToCamel

function doLowerLine(previousValue, currentValue, currentIndex, array){
 if(/[AZ]/.test(currentValue)){
  currentValue = currentValue.toLowerCase();
  if(currentIndex===0){
   return previousValue + currentValue;
  }else{
   return previousValue + '_' + currentValue;
  }
 }else{
  return previousValue + currentValue;
 }
}
function toLowerLine(arr){
 if(typeof arr === 'string'){
  arr = arr.split('');
 }
 return arr.reduce(doLowerLine,'');
}
var a = 'TestToLowerLine';
var res1 = toLowerLine(a); //test_to_lower_line
var res2 = [].reduce.call(a,doLowerLine,''); //test_to_lower_line

function doCamel(previousValue, currentValue, currentIndex, array){
 if(currentValue === '_'){
  return previousValue + currentValue.toUpperCase();
 }else{
  return previousValue + currentValue;
 }
}
function toCamel(str) {
 if(typeof str === 'string'){
  str = str.split(''); //Convert to character array}
 return str.reduce(doCamel);
}
console.log(toCamel('test_to_camel')); //TestToCamel

function doLowerLine(val, index, arr){
 if(/[AZ]/.test(val)){
  if(index===0){
   return val.toLowerCase();
  }else{
   return '_'+val.toLowerCase();
  }
 }else{
  return val;
 }
}
function toLowerLine(arr){
 if(typeof arr === 'string'){
  return [].map.call(arr,doLowerLine).join('');
  // Array.prototype.map.call(arr, doLowerLine).join('');
 }else{
  return arr.map(doLowerLine).join('');
 }
}
var a = 'TestToLowerLine';
var res1 = [].map.call(a,doLowerLine).join(''); //test_to_lower_line
var res2 = toLowerLine(a); //test_to_lower_line

var s = "fooStyleCss";
s = s.replace(/([AZ])/g,"-$1").toLowerCase();
//Use regular expressions to replace, concise and clear, great

var s1 = "foo-style-css";
s1 = s1.replace(//-(/w)/g, function(all, letter){
          return letter.toUpperCase();
        });
//I don't quite understand this part 2.

var s = "style-sheet-base";

var a = s.split("-");
var o = a[0];
for(var i=1;i<a.length;i++){
    o = o + a[i].slice(0,1).toUpperCase() + a[i].slice(1);
}

var s1 = "style-sheet-base";
s1 = s1.replace(//-(/w)/g, function(x){return x.slice(1).toUpperCase();});