array-changes-async

Array diffing

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array-changes-async
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Readme

array-changes-async
This is an async port of array-changes, to allow for an equal and similar functions that accept a callback. This allows your equal and similar functions to be asynchronous.

Original readme from array-changes

A library for finding differences between two arrays.
The library was extracted from unexpected and is therefore not documented and tested properly :-S
(Edit: This async version of the library actually has some more tests, not many, but some :)

Usage

var arrayChangesAsync = require('array-changes-async');

var leftArray = [ 1, 2, 4 ]
var rightArray = [ 1, 2, 3, 4 ]

function equal(a, b, aIndex, bIndex, callback) {
   // a is the value from the leftArray, aIndex is the index of that item
   // b is the value from the rightArray, bIndex is the index of the item
   // Call the callback function with `true` if a and b are considered equal
   callback(a === b);
}


arrayChangesAsync(leftArray, rightArray, equal, null /* see below */, function (result) {
    
    // result == [ 
    //   { 
    //      type: 'equal', value: 1
    //   },
    //   { 
    //      type: 'equal', value: 2
    //   },
    //   { 
    //      type: 'insert', value: 3
    //   },
    //   { 
    //      type: 'equal', value: 4
    //   }
    // ]
});

The fourth parameter allows to define 'similar' items, which has the same signature as the equal function, and allows to define what is considered similar, ie. 'changed', rather than deleted, and the expected value inserted.
The callbacks receive the aIndex and bIndex parameters, to allow for memoization, as some items will be tested for equality more than once. This is obviously more useful if you have an async equal function that could be expensive.