Replace on:click="reference" to addEventListener('click', reference) if given a DOM node and an object of named functions like {reference: event => alert(1)}

on-atttributes.js

function onAttributes(node = document.createElement('span'), functions = {}) {
  if (
    node.attributes
    && node.attributes.length
  ) {
    Array.from(node.attributes)
      .filter(({name}) => name.startsWith('on:'))
      .forEach(({name, value}) => {
        node.addEventListener(
          name.replace(/^on:/, '').toLowerCase(),
          functions[value]
        )

        node.removeAttribute(name)
      })
  }

  return node
}