Rec

Rec is a foundational library for implementing undo, redo, diffing, and event systems in JavaScript.

Benefits:

• No dependencies.
• Extensively tested.
• Less than 100 lines long.

Installation

npm install rec-js

Usage

The entire library is in rec.ts.

D

There are four types of deltas:

• Insert - Insert a value into an Object or Array at the given key.
• Update - Set a value in an Object or Array to a new value.
• Delete - Delete a value from an Object or Array.
• Compound - A compound of the three earlier types of D.

Apply

All deltas must be applied through the Apply function.

Apply(o : O, d : D) : O

An O is an Object. A D is a delta. Apply applies the D to the O argument.

Apply returns the same O after modification, for convenience. The object is modified by reference. It's not a new object.

let o = {}; // this could be any object - it doesn't have to be empty

let d = { type: INSERT, path : ["foo"], v : 12 };
o = Apply(o, d);
console.log(o); // prints { "foo" : 12 }

Invert

The Invert function inverts any D. You can only invert a D after it has been applied. Continuing from the example above:

let dinverse = Invert(d);
o = Apply(o, dinverse);
console.log(o); // prints {}

Building

npm run build

Testing

Rec has been extensively tested by deterministic, random test generation. The test suite runs >10k unique tests.

To run the tests:

npm test