camel-to-kebab.js

let _str = (function(){
    const tag = document.createElement('span')
    return   {
      propToAttr: (string) {
        tag.dataset[string] = true
        return tag.attributes[0].name.split(/^data-/)[1]
      },
      attrToProp(string) {
        tag.setAttribute(`data-${string}`, true)
        return Object.entries(tag.dataset)[0][0]
      }
    }
}())

kebab-to-camel.js

function kebabToCamel(string) {
  const tag = document.createElement('span')
  tag.setAttribute(`data-${string}`, true)
  return Object.entries(tag.dataset)[0][0]
}