Historian

"The present is the least important time we live in" --Alan Kay

A drop-in atom-state-management (UNDOs!!) for your clojurescript projects.

Also supports clojure in case you would want to make similar applications, or simply for testing.

Table of contents

Usage
Passive Atoms Shortcuts
Replacing Historian atoms

Usage

Add the following dependency in your project.clj:

And require historian in your namespace:

(ns my-ns
  (:require [historian.core :as hist]))

Suppose you have your state in an atom my-state:

(def my-state (atom "ABC"))

To keep an history of all changes, simply add your atom to historian:

(hist/record! my-state :my-state)

;; then change the state of your atom

(reset! my-state "DEF")

@my-state
=> "DEF"

(hist/undo!)

@my-state
=> "ABC"

(hist/redo!)

@my-state
=> "DEF"

;; tada!

Of course, sometimes we want to do some things without anyone noticing...

;; our current state is "ABC"

(hist/off-the-record
 (reset! my-state "GHI"))  ;; <--- this change won't be added to the undo history

(reset! my-state "ZZZ")

(hist/undo!)

@my-state
=> "ABC"

If you have a bunch of operations initiated by a single user action:

(hist/with-single-record
 (doseq [i (range 200)]
  (reset! my-state i)))
;; We've just done 200 operations on the atom, but only the last state is recorded.

(hist/undo!)

@my-state
=> "ABC"

You can also use the with-single-before-and-after macro to conditionally add a before AND after state when a non passive atom is modified. This is useful to snapshot the very last state of all passive atoms just before a normal atom is modified.

To check if any undo/redo history is available, use can-undo? and can-redo?.

When loading an app with multiple atoms, you should use clear-history! and trigger-record! to start with a clean slate.

Passive Atoms

When using record! on an atom, you can provide the optional passive? argument. A passive atom will not trigger any new save if modified. It will only be recorded if any other watched atom is modified."

(hist/record! my-state :my-state :passive)

Keyboard Shortcuts (cljs)

You can bind ctrl-z and ctrl-y to undo and redo by using bind-keys in the historian.keys namespace.

Replacing Atoms

You might need to replace the atoms in which Historian stores its data. (Say, for example, to make them compatible with [Reagent] (https://github.com/holmsand/reagent)).

(ns some-ns (:require [reagent.core :refer [atom]]
                      [historian.core :as hist]))

;; for undos:
(hist/replace-library! (atom [])) ; <----- the new atom must be a vector.

;; for redos:
(hist/replace-prophecy! (atom [])) ; <----- the new atom must be a vector.