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Symmetry

Create diffs between two values:

a = { x: 3, y: 5, z: 1 };
b = { x: 3, y: 8, z: 1 };
patch = createPatch(a, b);
// => { t: 'o', s: { y: 8 } }

a = ["one", "two", "three"];
b = ["one", "two", "two and a half"];
patch = createPatch(a, b);
// => { t: 'a', s: [ [2, 1, 'two and a half'] ] }

And apply them somewhere else:

obj = { x: 3, y: 5, z: 1 };
patch = { t: "o", s: { y: 8 } };
after = applyPatch(obj, patch);
// => { x: 3, y: 8, z: 1 }

Will diff anything with a toJSON() method.

people = new Backbone.Collection([
  { id: 1, name: "John", age: 30 },
  { id: 2, name: "Dave", age: 34 },
]);

before = people.toJSON();
people.add({ id: 3, name: "Mark", age: 27 });
people.get(2).set("age", 35);
patch = createPatch(before, people);
// => {
//   t: "a",
//   p: { 1: { t: "o", s: { age: 35 } } },
//   s: [[2, 0, { id: 3, name: "Mark", age: 27 }]]
// }

MIT-licensed

Installing

Install using NPM:

npm install symmetry

Patch format

Patches are one of three types of object, identified by the t field.

Object patches have "t": "o", and additional fields:

  • r for 'remove', with a list of target properties to remove.
  • s for 'set', with an object mapping target properties to values.
  • p for 'patch', with an object mapping target properties to subpatches.

Array patches have "t": "a", and additional fields:

  • p for 'patch', with an object mapping target indices to subpatches.
  • s for 'splice', with a list of argument lists for the array splice method to apply in order. Must be applied after p.

Reset patches have "t": "r", and additional fields:

  • v for 'value', containing the new value in full.

Reset patches occur when two values differ enough to make a patch not useful.

Finally, a patch may also be null to indicate no change.

Hacking the code

git clone https://github.com/Two-Screen/symmetry.git
cd symmetry
npm install
npm test