Temporal Composability

Undo / Redo in angular with promises and the command pattern

Image by Gossins: Flow of Time

Undo / Redo

Native apps (including browser) support undo

Web apps and Mobile apps do not Power users produce more errors than

consumers Power users on a computer with native app What happens when a power user uses a

web app?

Power User

I want to be able to build a collection I want to be able to undo a price change

without having to remember which price I destroyed.

Use Case

Sets all items to 222% margin

function

x f(x)

invertable

x f(x)

f-1(f(x))

State Machine

Dual Transitions

Command Pattern

Double Stack

Double Stack

asdf

Creating a collection ID is returned asynchronously as a promise ID not specified until after creation but

needed for deletion

Discontinuity

*Each function has the result of its inverse as input

Promises and double closure

msg

Results Promise

Context

Arguments

Function

Results Promise

inversemsg

Promises

F -> $q(f) - Function that generates a promise (reuse allows for unlimited undo/redo)

Asynchronous actions are handled (composition)

Anything can undo/redo if providing 2 functions

User messaging for current state of undo/redo

Reusablility & Composiblity

Answers & Questions