Mut.js - efficient DOM writing via mutation and version flag

mut.js

const $version = Symbol('version')

export const version = state => {
  if state[$version] == null {
    return 0
  }
  return state[$version]
}

export const markSynced = (following, leading) => {
  following[$version] = version(leading)
}

// Bump the state version
export const bump = state => {
  let next = version(state) + 1
  state[$version] = next
  return next
}

// Mutate state with a set function.
// If set function returns true, then state is marked dirty.
export const mut = (set, state, value) => {
  let isDirty = !!set(state, value)
  if (isDirty) {
    bump(state)
  }
  return isDirty
}

// Write if dirty, using a `write` function.
export const patch = (
  write,
  element,
  state,
  send
) => {
  if (state[$version] === element[$version]) {
    return
  }
  write(element, state, send)
  markSynced(element, state)
}