A `beforeonunload` emulator for Mithril

BeforeUnload.js

function BeforeUnload(){
  const route.  = m.route.set
  const handler = e => {
    if(
      e.target.href 
      && 
      e.target != '_blank' 
      && 
      !confirm(message)
    ){
      // Need to prevent (native behaviour) & stop (Mithril bindings)
      e.preventDefault()
      e.stopPropagation()
    }
  },
  
  return {
    view: () => {},
    
    oncreate: ({attrs: {message = 'Are you sure?'}}) => {
      addEventListener('click', handler, true)
      
      m.route.set = function(){
        if(confirm(message))
          return route.apply(this, arguments)
      }
    },

    onremove: () => {
      removeEventListener('click', handler, true)
      
      m.route.set = route
    },
  }
}