What's wrong with this?

diffm.js

export default (component, previous = undefined) => ({
    ...component,

    onbeforeupdate: (a, b) => (
        component.onbeforeupdate 
      &&
        component.onbeforeupdate(a, b) !== false
      &&
        previous = b 
    ),

    ...['view', 'onupdate', 'onbeforeremove', 'onremove']
      .filter(
        key => component[key]
      )
      .reduce(
          (lifecycle, key) => ({
            ...lifecycle,
            [key] : current => 
              component[key](current, previous),
          })
        ,
          {}
      )
    ,
  })