Brauhaus.js Diff Plugin

A plugin for Brauhaus.js that adds diff functionality.

Installation

There are two ways to use Brauhaus-Diff - either in a web browser (client-side) or on e.g. Node.js (server-side).

Web Browser (client-side use)

To use Brauhaus-Diff in a web browser, simply download the following files and include them as you would any other script:

• Download the latest brauhaus.min.js
• Download the latest brauhaus-diff.min.js
• Download the latest murmurhash.js or a minified version

<script type="text/javascript" src="/scripts/murmurhash.js"></script>
<script type="text/javascript" src="/scripts/brauhaus.min.js"></script>
<script type="text/javascript" src="/scripts/brauhaus-diff.min.js"></script>
<script type="text/javascript">
    // Your code goes here!
    // See below for an example...
</script>

Node.js (server-side use)

For Node.js, you can easily install Brauhaus-Diff using npm:

npm install brauhaus-diff

Quick Example (Diff)

// The following lines are NOT required for web browser use
var Brauhaus = require('brauhaus');
require('brauhaus-diff');

// Create two recipes to compare
var left = new Brauhaus.Recipe({
    description: 'A recipe that makes little sense',
    boilSize: 12
});
left.add('fermentable', {
    name: 'Test Fermentable',
    late: true,
    yield: 70
});
left.add('fermentable', {
    name: 'Other Fermentable',
    weight: 2.2
});
left.add('spice', {
    name: 'Test spice',
    weight: 1,
    time: 45,
    use: 'smelt'
})
left.add('yeast', {
    name: 'Yeast',
    form: 'solid'
});

var right = new Brauhaus.Recipe({
    description: 'TODO'
});
right.add('fermentable', {
    name: 'Other Fermentable',
    yield: 20
})
right.add('spice', {
    name: 'Random spice'
})
right.add('yeast', {
    name: 'Yeast'
})

// Calculate the diff
var diff = Brauhaus.Diff.diff(left, right);

// Print the diff in Node.js
console.log(util.inspect(diff, false, null));

// Diff looks like:
// { description: { left: 'A recipe that makes little sense', right: 'TODO' },
//   boilSize: { left: 12, right: 10 },
//   fermentables: 
//    { diff: 
//       [ { weight: { left: 2.2, right: 1 },
//           yield: { left: 75, right: 20 },
//           _h: { left: '1o4wdgh', right: 'sx87wo' } },
//         { name: 'Test Fermentable',
//           weight: 1,
//           yield: 70,
//           color: 2,
//           late: true,
//           _h: { left: '158d476', right: null } } ] },
//   spices: 
//    { diff: 
//       [ { name: 'Test spice',
//           weight: 1,
//           aa: 0,
//           use: 'smelt',
//           time: 45,
//           form: 'pellet',
//           _h: { left: '1uctkbv', right: null } },
//         { name: 'Random spice',
//           weight: 0.025,
//           aa: 0,
//           use: 'boil',
//           time: 60,
//           form: 'pellet',
//           _h: { left: null, right: '1us1ios' } } ] },
//   yeast: 
//    { diff: 
//       [ { form: { left: 'solid', right: 'liquid' },
//           _h: { left: 'mfcqxm', right: '16drowi' } } ] } }

// Or when converted to JSON and formatted (slightly less verbose):
// { description: ["A recipe that makes little sense", "TODO"],
//   boilSize: [12, 10],
//   fermentables: [
//      { weight: [2.2, 1],
//        yield: [75, 20],
//       _h: ["1o4wdgh", "sx87wo"] },
//      { name: "Test Fermentable",
//        weight: 1,
//        yield: 70,
//        color: 2,
//        late: true,
//        _h: ["158d476", null] } ],
//   spices: [
//      { name: "Test spice",
//        weight: 1,
//        aa: 0,
//        use: "smelt",
//        time:45,
//        form: "pellet",
//        _h: ["1uctkbv", null] },
//      { name: "Random spice",
//        weight: 0.025,
//        aa: 0,
//        use: "boil",
//        time: 60,
//        form: "pellet",
//        _h: [null, "1us1ios"] } ],
//   yeast: [
//      { form: ["solid", "liquid"],
//        _h: ["mfcqxm", "16drowi"] } ] }

Quick Example (Applying changes)

// The following lines are NOT required for web browser use
var Brauhaus = require('brauhaus');
require('brauhaus-diff');

// Create diff
// ... (see above example)

// Apply changes backward (go from left to right)
var recipe = Brauhaus.Diff.apply(left, diff);

// Print the new recipe in Node.js
console.log(util.inspect(recipe, false, null));

// Apply the changes forward (go from right to left)
recipe = Brauhaus.Diff.apply(right, diff, 'forward');

// Print the new recipe in Node.js
console.log(util.inspect(recipe, false, null));

Quick Example (Converting to/from JSON)

// The following lines are NOT required for web browser use
var Brauhaus = require('brauhaus');
require('brauhaus-diff');

// Create diff
// ... (see above example)

// Serialize to JSON
var json = JSON.stringify(diff);

// Deserialize from JSON
var diff = Diff.parse(json);
// or
var obj = JSON.parse(json);
diff = Diff.parse(obj);

Diff Configuration

Several global options are available for configuring how Brauhaus-Diff works. These options can be passed into Brauhaus.Diff.configure() as an object, e.g.

Brauhaus.Diff.configure({
    usingBrauhausStyles: true
});

| Option | Type | Default | Description | | ------------------- | ------- | ------- | ----------- | | exportUtil | boolean | false | Export internal utility functions as Brauhaus.Diff.util. This is primarily intended for debugging purposes. | | usingBrauhausStyles | boolean | depends | When diffing or applying changes to recipes, check if the style is one of the known styles. If so, some info from the diff can be dropped. This option defaults to true if the Brauhaus-Styles plugin is loaded before Brauhaus-Diff, and false otherwise. | | removeDefaultValues | boolean | false | Some Brauhaus objects use defaults supplied by their prototypes. If set to true, the diff will check whether values are different from default when adding or removing one of these objects. This option is disabled by default because it may remove useful information from the diff if you aren't sure what the prototype chain will be when you apply the changes to another object. If you only plan on diffing recipes, this option can be safely enabled to save some space in the diffs. |

An example of the difference from removeDefaultValues:

// Create a Fermentable
var fermentable = new Brauhaus.Fermentable({
    weight: 2
});

// Run the diff with the option disabled
Brauhaus.Diff.configure({
    removeDefaultValues: false
});
Brauhaus.Diff.diff(fermentable, null)
// { left: 
//    { name: 'New Fermentable',
//      weight: 2,
//      yield: 75,
//      color: 2,
//      late: false },
//   right: null }

// Run the diff with the option enabled
Brauhaus.Diff.configure({
    removeDefaultValues: true
});
Brauhaus.Diff.diff(fermentable, null)
// { left:
//    { name: 'New Fermentable',
//      weight: 2 },
//   right: null }

Brauhaus.Diff

Diff.diff (left, right)

Compute the difference between left and right, which can be primitive types, arrays, or objects. A diff object is returned which can be serialized or used to apply changes to other objects. If no changes are found, an empty object is returned.

Brauhaus-Diff treats arrays differently based on their contents. Arrays containing only objects are treated as unordered collections where matches are searched for between left and right, while arrays containing mixed types are treated as simple ordered lists with pairwise diffing. See the sections on Using Custom Types and Diff Format for more details.

For the purposes of Diff.apply, left is considered the newer object such that applying a diff forward means turning a right object into a left object, while applying a diff backward does the opposite. See Diff.apply for more details.

Diff.apply (applyTo, diff, [direction], [fail])

Apply a diff to an object, array, or primitive type (applyTo), optionally supplying a diff direction and failure mode. A copy of applyTo is returned with the modifications from diff.

Diff can be a single diff object, a single JSON string, an array of diff objects, or an array of JSON strings. If multiple diffs are used, the diffs are applied to the object in the order of iteration. The direction parameter specifies the direction of the diff, i.e. is applyTo on the left (backward) or right (forward), not the direction of iteration for multiple diffs. So when applying the diff backward (left-to-right), the order of iteration must be left-most first; when applying forward (right-to-left), the order of iteration must be right-most first. An example of valid inputs:

// A single diff object
var diff = Brauhaus.Diff.diff(1, 2);
Brauhaus.Diff.apply(1, diff);
// Returns 2

// Multiple diff objects
diff = [Diff.diff(1, 2), Brauhaus.Diff.diff(2, 3)];
Brauhaus.Diff.apply(1, diff);
// Returns 3

// A single JSON string
var diff = '[1, 2]';
Brauhaus.Diff.apply(1, diff);
// Returns 2

// Multiple JSON strings
var diff = ['[1, 2]', '[2, 3]'];
Brauhaus.Diff.apply(1, diff)
// Returns 3

Direction is the direction to apply the diff. The two basic options are turning a right object into a left object (forward diff) and turning a left object into a right object (backward diff, default). The valid inputs options for direction are:

• 'backward', 'b', 'leftToRight', 'left-to-right', 'ltor', or 'l' for a backward diff
• 'forward', 'f', 'rightToLeft', 'right-to-left', 'rtol', or 'r' for a forward diff

Fail is either a boolean indicating the failure mode or a failure function. Whenever apply encounters an inconsistency between applyTo and diff, it consults fail for what to do. Inconsistencies can occur when a value in applyTo doesn't match the expected value from diff, when an object is missing or already present, etc. When fail is false, all inconsistencies are ignored. When fail is true (default) and an inconsistency is found, apply will throw an exception with the following properties:

• e instanceof Error === true
• e.message The error message
• e.keys An array containing the nested object keys where the inconsistency was found
• e.expected The expected value
• e.actual The actual value

When fail is a function, whether apply throws an exception depends on the return value of the function. If the function returns true an exception is thrown, otherwise it is ignored. The fail function should accept up to three parameters: keys, expected, and actual, with the same definitions as above. An example of using a fail function:

// Causes a failure if the inconsistency is in a nested object, but allows
// inconsistencies in a top-level object
function fail(keys, expected, actual) {
    return keys.length > 1
}

// Create some objects to diff
var left = {
    a: 1,
    b: {
        x: 5,
        y: 6 } };
var right = {
    a: 2,
    b: {
        x: 5,
        y: 7 } };
var diff = Brauhaus.Diff.diff(left, right);

// No failure function, exception will be thrown
Brauhaus.Diff.apply({
    a: 2,
    b: {
        x: 5,
        y: 6 } },
diff, 'backward');
// Error: Diff encountered an inconsistency (key: a, expected: 1, actual: 2)

// Using the fail function for the same input
Brauhaus.Diff.apply({
    a: 2,
    b: {
        x: 5,
        y: 6 } },
diff, 'backward', fail);
// { a: 2,
//   b: {
//      x: 5,
//      y: 7 } }

// Using the fail function with a nested inconsistency
Brauhaus.Diff.apply({
    a: 2,
    b: {
        x: 5,
        y: 3 } },
diff, 'backward', fail);
// Error: Diff encountered an inconsistency (key: b.y, expected: 6, actual: 3)

apply may also fail for reasons that are not handled by the failure mode / function; for instance trying to apply an object diff to a non-object, or an object array diff to a non-array. In those cases, an Error object is always thrown.

Diff.parse (object/json)

Convert JSON or a diff-like object into a diff object that can be applied. The diff-like objects supported are the same as Brauhaus-Diff serializes. See the section on Diff Format for more details.

Brauhaus.Recipe Support

Brauhaus-Diff can be used for many generic objects, but it has special support for Recipes (and by extension, Fermentables, Spices, Yeasts, and MashSteps). This support includes:

• Brauhaus-Styles plugin support (see Diff Configuration section)
• Use in object arrays
• Constructing the correct type on created sub-objects
• Diff only the properties that will be serialized

The next section covers adding these features to custom types.

Using Custom Types

For simple objects that will not be used in arrays, nothing extra needs to be done to diff them. Several examples throughout this document show how this can be done, but it's as simple as Brauhaus.Diff.diff(left, right).

Use in object arrays

To use objects in arrays and have them matched between left and right, a set of keys needs to be set on the object or its prototype. The keys property is called _diffKeys, and its value must be an array that contains only arrays and strings. The keys in the array are matched sequentially in the order of iteration, with each subsequent key being considered less important than the previous key. An example to illustrate:

Brauhaus.Fermentable.prototype._diffKeys = ['name', 'late', ['weight', 'color', 'yield']];

When a Fermentable is included in an array, the diff algorithm will look in both left and right for matching names. If a single match is found in both sides, the values are paired and diffed. If no match is found, the value is considered an addition or deletion from the list. If multiple matches are found, the algorithm continues to the next key, late, and tries to pick the best match for each value. If multiple values have the same late property, the diff algorithm goes to the weight, color, and yield key. When a key is complex like this, the diff algorithm bases the match on the number of correct key/value combinations in the complex key. Both the key and value must match for the key/value pair to be considered equal. If two matches are found to be equally good, the diff algorithm simply picks the first choice available.

Note that two objects with different primary keys (the first key) will never be paired. However, objects with the same primary key but different secondary keys may be paired.

By setting diff keys on an object or its prototype, all of this matching will be done automatically by the diff algorithm. However, diff arrays of objects without keys will likely result in poor matches and unexpected output.

Constructing sub-objects

By default, objects constructed by Brauhaus-Diff will have only Object in their prototype chain. In order to construct objects of a given type, a special property must be set on the object passed into apply or its prototype, called _paramMap. This property must be an object whose keys are the keys to which special construction should be applied, and whose values are constructors to use. An example to illustrate from Brauhaus.Recipe:

Brauhaus.Recipe.prototype._paramMap = {
    fermentables: Brauhaus.Fermentable,
    spices: Brauhaus.Spice,
    yeast: Brauhaus.Yeast,
    mash: Brauhaus.Mash
};

Whenever a Recipe is diffed and a new object is created under the fermentables key, for instance, the created object is passed to the Brauhaus.Fermentable constructor via new Brauhaus.Fermentable(createdObject). The constructor should accept an object that looks like an instance of the requested type, and return a copy of that object with the right type. To see how Brauhaus accomplishes this, take a look at Brauhaus.OptionConstructor. Depending on your type, it could be as simple as:

function MyType(obj) {
    for (key in obj) {
        this[key] = obj[key];
    }
}

Diff only certain properties

Brauhaus-Diff checks whether an object contains a toJSON function before applying the diff. If the function exists, the diff will be performed on the object returned by calling toJSON() instead of the object itself. This allows for diffing only the properties that would be serialized to JSON for the object, instead of all properties on the object.

If this behavior is undesirable, the toJSON function should be removed or replaced with a non-function, or a copy of the object without the function should be passed to Diff.diff. This may change in the future to use another function instead of toJSON.

Perform custom post-diff functions

While performing a diff, every changed object is checked for a postDiff function on itself, its prototype, and its constructor, in that order. If the function is found, it will be called with the left and right values, along with the diff. This function can modify the diff object if desired. If both left and right would call the same postDiff function, it will only be called once, otherwise the function for both objects will be called. An example from Brauhaus.Recipe (modified for readability):

Brauhaus.Recipe.postDiff = function(left, right, diff) {
    if (Options.usingBrauhausStyles && diff.style) {
        if (diff.style instanceof ValueDiff) {
            if (diff.style.left.name && diff.style.left.category)
                if (getStyle(diff.style.left.category, diff.style.left.name))
                    cleanStyle(diff.style.left);

            if (diff.style.right.name && diff.style.right.category)
                if (getStyle(diff.style.right.category, diff.style.right.name))
                    cleanStyle(diff.style.right);

        } else {
            var leftName = diff.style.name.left || left.style.name;
            var leftCategory = diff.style.category.left || left.style.category;
            var rightName = diff.style.name.right || right.style.name;
            var rightCategory = diff.style.category || right.style.category;
            if (getStyle(leftCategory, leftName) && getStyle(rightCategory, rightName))
                cleanStyle(diff.style);
        }
    }
};

Whenever a recipe is diffed, the above code checks to see whether the style was changed and, if so, whether the style information can be reconstructed from the Brauhaus.Styles plugin. If only known styles are being used, the other properties ( gu, fg, srm, etc.) are removed from the diff.

Perform custom post-apply functions

Like postDiff, applying changes checks for a postApply function that accepts the modified object and the diff passed to apply. Any special changes may be made to the object in this function.

Unexpected Output

If the diff output isn't what you expected, there are several possible reasons:

• Check the Diff Configuration to make sure it's what you wanted.
• If you're diffing arrays of objects, make sure they have their diff keys set (see Using Custom Types).
• Diffing different types will always result in removing one and adding the other, including diffing an array vs. an object (even with the same keys).
• You found a bug, please submit a bug report if you have the chance.

Diff Format (JSON)

The diff format saved to JSON is fairly simple, consisting of only three types: a value diff, an object diff, and an object array diff.

Value Diff

Value diffs are simple [left, right] pairs of values. They represent a value difference or replacement.

Object Diff

Object diffs are objects whose keys are the properties that were changed, and whose values are another diff object. They are used when comparing two objects, and are simply a container for the changes. Brauhaus-Diff does not distinguish between keys that are missing, keys that are set to undefined, and keys set to null; they are all considered equal to null. This means that Brauhaus-Diff will never delete keys on an object when applying changes, but it may set them to null. If you need keys deleted, you will need to delete them manually after applying a diff. An example of an object diff:

var left = {
    a: 1,
    b: {
        x: 5,
        y: 6 } };
var right = {
    a: 2,
    b: {
        x: 5,
        y: 7 } };
Brauhaus.Diff.diff(left, right);
// { a: [1, 2],
//   b: {
//      y: [6, 7] } }
// The arrays [1, 2] and [6, 7] are Value Diffs representing the changes

Arrays of mixed types are considered objects for the purposes of diffing, and result in an object diff with numerical keys.

Object Array Diff

Arrays of objects are represented exactly as such with the addition of an _h key on each of the contained objects or object diffs. The _h key contains a value diff with hashes for the left and right objects, which are needed to find the correct object to which to apply changes. Array values are either an object diff (if left and right both contain the object), or simply a copy of the object (if the object only exists in left or right). An example of an object array diff:

var left = [];
left.push(new Brauhaus.Fermentable({
    name: 'fermentable',
    weight: 2
}));

var right = [];
right.push(new Brauhaus.Fermentable({
    name: 'fermentable'
}));
right.push(new Brauhaus.Fermentable({
    name: 'other',
    yield: 70
}));

Brauhaus.Diff.diff(left, right);
// [ { weight: [2, 1],
//     _h: ["u47usq", "1s5bg5s"] },
//   { name: "other",
//     yield: 70,
//     _h: [null, "cxt9ff"] } ]
//
// The first element is an Object Diff
// The second element is just a copy of right[1] with the extra _h key

Contributing

Contributions are welcome - just fork the project and submit a pull request when you are ready!

Getting Started

First, create a fork on GitHub. Then:

git clone ...
cd brauhaus-diff
npm install

Style Guide

Brauhaus uses the CoffeeScript Style Guide with the following exceptions:

1. Indent 4 spaces
2. Maximum line length is 120 characters

When building brauhaus-diff.js with cake build or npm test you will see the output of CoffeeLint, a static analysis code quality tool for CoffeeScript. Please adhere to the warnings and errors to ensure your changes will build.

Unit Tests

Before submitting a pull request, please add any relevant tests and run them via:

npm test

If you have PhantomJS installed and on your path then you can use:

CI=true npm test

Pull requests will automatically be tested by Travis CI both in Node.js 0.8/0.10 and in a headless webkit environment (PhantomJS). Changes that cause tests to fail will not be accepted. New features should be tested to be accepted.

New tests can be added in the test directory. If you add a new file there, please don't forget to update the test.html to include it!

Code Coverage

You can generate a unit test code coverage report for unit tests using the following:

cake coverage

You can find an HTML report in the coverage directory that is created. This report will show line-by-line code coverage information.

Please note that all contributions will be licensed under the MIT license in the following section.

License

Copyright (c) 2013 Jens Taylor

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.