Convert kebab-case to camelCase - Javascript

You can also try regex.

camelize = s => s.replace(/-./g, x=>x.toUpperCase()[1])

Looks only for hyphen followed by any character, and capitalises it and replaces the hyphen+character with the capitalised character.

To keep your existing code, I've just added a check on the index that will return item instead of the transformed item if item is 0 (falsy), since the problem is just that you are upper-casing the first item as well, while you shouldn't.

In a nutshell, the inline expression becomes: (item, index) => index ? item.charAt(0).toUpperCase() + item.slice(1).toLowerCase() : item, because:

• If index is not falsy (so, if index is > 0 in your context), the capitalized string is returned.
• Otherwise, the current item is returned.

Of course, this could be cleaner and likely single line, but I wanted to stay as close as possible to your code so that you could understand what was wrong:

function camelize(str){
  let arr = str.split('-');
  let capital = arr.map((item, index) => index ? item.charAt(0).toUpperCase() + item.slice(1).toLowerCase() : item.toLowerCase());
  // ^-- change here.
  let capitalString = capital.join("");

  console.log(capitalString);
}

camelize("my-kebab-string");

As a side note, you could've found a potential cleaner answer here: Converting any string into camel case

The first method is to just transform to lower case the first entry of your capital array, like this:

capital[0] = capital[0].toLowerCase();

Another method, which I think to be more efficient, is to pass another parameter to the map callback, which is the index. Take a look at this for further reading: https://www.w3schools.com/jsref/jsref_map.asp

So you transform to upper case only if (index > 0). Like this:

let capital = arr.map((item, index) => index ? item.charAt(0).toUpperCase() + item.slice(1).toLowerCase() : item);