en.javascript.info/1-js/4-data-structures/8-array-methods/1-camelcase/_js.view/solution.js

function camelize(str) {
  return str
    .split('-') // my-long-word -> ['my', 'long', 'word']
    .map( 
      (word, index) => index == 0 ? word : word[0].toUpperCase() + word.slice(1)
    ) // ['my', 'long', 'word'] -> ['my', 'Long', 'Word']
    .join(''); // ['my', 'Long', 'Word'] -> myLongWord
}