Collections

This package contains JavaScript implementations of common data structures with idiomatic iterfaces, including extensions for Array and Object.

• List(values, equals, getDefault)

  An ordered collection of values with fast insertion and deletion and forward and backward traversal, backed by a cyclic doubly linked list with a head node. Lists support most of the Array interface, except that they use and return nodes instead of integer indicies in analogous functions.

  Lists have a head Node. The node type is available as Node on the list prototype and can be overridden by inheritors. Each node has prev and next properties.

• Set(values, equals, hash, getDefault)

  A collection of unique values. The set can be iterated in the order of insertion. With a good hash function for the stored values, insertion and removal are fast regardless of the size of the collection. Values may be objects. The equals and hash functions can be overridden to provide alternate definitions of "unique". Set is backed by FastSet and List.

• Map(map, equals, hash, getDefault)

  A collection of key and value items with unique keys. Keys may be objects. The collection iterates in the order of insertion. Map is backed by Set.

• MultiMap(map, getDefault, equals, hash)

  A collection of keys mapped to collections of values. The default getDefault collection is an Array, but it can be a List or any other array-like object. MultiMap inherits Map but overrides the getDefault(key) provider.

• WeakMap()

  A non-iterable collection of key value pairs. Keys must objects and do not benefit from hash functions. Some engines already implement WeakMap. The non-iterable requirement makes it possible for weak maps to collect garbage when the key is no longer available, without betraying when the key is collected. The shimmed implementation undetectably annotates the given key and thus does not necessarily leak memory, but cannot collect certain reference graphs. This WeakMap shim was implemented by Mark Miller of Google.

• SortedSet(values, equals, compare, getDefault)

  A collection of unique values stored in stored order, backed by a splay tree. The equals and compare functions can be overridden to provide alternate definitions of "unique".

• SortedMap(map, equals, compare, getDefault)

  A collection of key value pairs stored in sorted order. SortedMap is backed by SortedSet and the GenericMap mixin.

• LruSet(values, maxLength, equals, hash, getDefault)

  A cache with the Least-Recently-Used strategy for truncating its content when it’s length exceeds maxLength. LruSet is backed by a Set and takes advantage of the already tracked insertion order. Both getting and setting a value constitute usage, but checking whether the set has a value and iterating values do not.

• LruMap(map, maxLength, equals, hash, getDefault)

  A cache of items backed by an LruSet.

• SortedArray(values, equals, compare, getDefault)

  A collection of values stored in a stable sorted order, backed by an array.

• SortedArraySet(values, equals, compare, getDefault)

  A collection of unique values stored in sorted order, backed by a plain array. If the given values are an actual array, the sorted array set takes ownership of that array and retains its content. A sorted array set performs better than a sorted set when it has roughly less than 100 values.

• SortedArrayMap(values, equals, compare, getDefault)

  A collection of key value pairs stored in sorted order, backed by a sorted array set.

• FastSet(values, equals, hash, getDefault)

  A collection of unique values stored like a hash table. The underlying storage is a Dict that maps hashes to lists of values that share the same hash. Values may be objects. The equals and hash functions can be overridden to provide alternate definitions of "unique".

• FastMap(map, equals, hash, getDefault)

  A collection of key and value items with unique keys, backed by a set. Keys may be objects. FastMap is backed by FastSet and the GenericMap mixin.

• Dict(values, getDefault)

  A collection of string to value mappings backed by a plain JavaScript object. The keys are mangled to prevent collisions with JavaScript properties.

• Iterator(iterable)

  A wrapper for any iterable that implements iterate or iterator the implements next, providing a rich lazy traversal interface.

• Array

  An ordered collection of values with fast random access, push, and pop, but slow splice. The array module provides extensions so it hosts all the expressiveness of other collections. The array-shim module shims EcmaScript 5 methods onto the array prototype if they are not natively implemented.

• Object

  Can be used as a mapping of owned string keys to arbitrary values. The object module provides extensions for the Object constructor that support the map collection interface and can delegate to methods of collections, allowing them to gracefully handle both object literals and collections.

Constructor Arguments

For all of these constructors, the argument values is an optional collection of initial values, and may be an array. If the values are in a map collection, the the values are taken, but the keys are ignored.

• map

  The map argument is an optional collection to copy shallowly into the new mapping. The map may be an object literal. If map implements keys, it is treated as a mapping itself and copied. Otherwise, if map implements forEach, it may be any collection of [key, value] pairs.

equals(x, y), compare(x, y), and hash(value) are all optional arguments overriding the meaning of equality, comparability, and consistent hashing for the purposes of the collection. equals must return a boolean. compare must return an integer with the same relationship to zero as x to y. hash should consistently return the same string for any given object.

• equals(x, y)

  The default equals operator is implemented in terms of ===, but treats NaN as equal to itself and -0 as distinct from +0. It also delegates to an equals method of either the left or right argument if one exists. The default equality operator is shimmed as Object.equals.

• compare(x, y)

  The default compare operator is implemented in terms of < and >. It delegates to the compare method of either the left or right argument if one exists. It inverts the result if it uses the falls to the right argument. The default comparator is shimmed as Object.compare.

• hash(value)

  The default hash operator uses toString for values and provides a Unique Label for arbitrary objects. The default hash is shimmed as Object.hash.

• getDefault(key or value)

  The default getDefault function is Function.noop, which returns undefined. The fallback function is used when you get a nonexistant value from any collection. The getDefault function becomes a member of the collection object, so getDefault is called with the collection as this, so you can also use it to guarantee that default values in a collection are retained, as in MultiMap.

Collection Methods

Where these methods coincide with the specification of an existing method of Array, Array is noted as an implementation. Array+ refers to shimmed arrays, as installed with the array module. Object refers to methods implemented on the Object constructor function, as opposed to the Object.prototype. Object+ in turn refers to methods shimmed on the object constructor by the object module. These functions accept the object as the first argument instead of the this implied argument. Strikethrough indicates an implementation that should exist but has not yet been made (Send a pull request!).

These are all of the collections:

(Array, Array+, Object+, Iterator, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• has(key)

  Whether a value for the given key exists.

  (Object+, Map, MultiMap, SortedMap, LruMap, SortedArrayMap, FastMap, Dict)

  has(value, opt_equals)

  Whether a value exists in this collection. This is slow for list (linear), but fast (logarithmic) for SortedSet and SortedArraySet, and very fast (constant) for Set.

  (Array+, List, Set, SortedSet, LruSet, SortedArray, SortedArraySet, FastSet)

• get(key or index)

  The value for a key. If a Map or SortedMap lacks a key, returns getDefault(key).

  (Array+, Map, SortedMap, SortedArrayMap, WeakMap, Object+)

  get(value)

  Gets the equivalent value, or falls back to getDefault(value).

  (List, Set, SortedSet, LruSet, SortedArray, SortedArraySet, FastSet)

• set(key or index, value)

  Sets the value for a key.

  (Map, MultiMap, WeakMap, SortedMap, LruMap, SortedArrayMap, FastMap, Dict)

• add(value)

  Adds a value. Ignores the operation and returns false if an equivalent value already exists.

  (Array+, List, Set, SortedSet, LruSet, SortedArray, SortedArraySet, FastSet)

  add(value, key)

  Aliases set(key, value), to assist generic methods used for maps, sets, and other collections.

• addEach(values)

  Copies values from another collection to this one.

  (Array+, List, Set, SortedSet, LruSet, SortedArray, SortedArraySet, FastSet)

  addEach(mapping)

  Copies items from another collection to this map. If the mapping implements keys (indicating that it is a mapping) and forEach, all of the key value pairs are copied. If the mapping only implements forEach, it is assumed to contain [key, value] arrays which are copied instead.

  (Object+, Map, MultiMap, SortedMap, LruMap, SortedArrayMap, FastMap, Dict)

• delete(key)

  Deletes the value for a given key. Returns whether the key was found.

  (Map, MultiMap, WeakMap, SortedMap, LruMap, SortedArrayMap, FastMap, Dict)

  delete(value)

  Deletes a value. Returns whether the value was found.

  (Set, SortedSet, LruSet, SortedArray, SortedArraySet, FastSet)

  delete(value, equals)

  Deletes the equivalent value. Returns whether the value was found.

  (Array+, List)

• deleteEach(values or keys)

  Deletes every value or every value for each key.

  (Array+, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• indexOf(value)

  Returns the position in the collection of a value, or -1 if it is not found. Returns the position of the first of equivalent values. For an Array this takes linear time. For a SortedArray and SortedArraySet, it takes logarithmic time to perform a binary search. For a SortedSet, this takes ammortized logarithmic time since it incrementally updates the number of nodes under each subtree as it rotates.

  (Array, List, SortedSet, SortedArray, SortedArraySet)

• lastIndexOf(value)

  Returns the position in the collection of a value, or -1 if it is not found. Returns the position of the last of equivalent values.

  (Array, List, SortedArray, SortedArraySet)

• find(value, opt_equals)

  Finds a value. For List and SortedSet, returns the node at which the value was found. For SortedSet, the optional equals argument is ignored.

  (Array+, List, SortedSet)

• findLast(value, opt_equals)

  Finds the last equivalent value, returning the node at which the value was found.

  (Array+, List, SortedArray, SortedArraySet)

• findLeast()

  Finds the smallest value, returning the node at which it was found, or undefined. This is fast (logarithmic) and performs no rotations.

  (SortedSet)

• findLeastGreaterThan(value)

  Finds the smallest value greater than the given value. This is fast (logarithic) but does cause rotations.

  (SortedSet)

• findLeastGreaterThanOrEqual(value)

  Finds the smallest value greater than or equal to the given value. This is fast (logarithmic) but does cause rotations.

  (SortedSet)

• findGreatest()

  (SortedSet)

• findGreatestLessThan(value)

  (SortedSet)

• findGreatestLessThanOrEqual(value)

  (SortedSet)

• push(...values)

  Adds values to the end of a collection.

  (Array, List)

  push(...values) for non-dequeues

  Adds values to their proper places in a collection. This method exists only to have the same interface as other collections.

  (Set, SortedSet, LruSet, SortedArray, SortedArraySet, FastSet)

• unshift(...values)

  Adds values to the beginning of a collection.

  (Array, List)

  unshift(...values) for non-dequeues

  Adds values to their proper places in a collection. This method exists only to have the same interface as other collections.

  (Set, SortedSet, LruSet, SortedArray, SortedArraySet, FastSet)

• pop()

  Removes and returns the value at the end of a collection.

  (Array, List, Set, SortedSet, LruSet, SortedArray, SortedArraySet)

• shift()

  Removes and returns the value at the beginning of a collection.

  (Array, List, Set, SortedSet, LruSet, SortedArray, SortedArraySet)

• slice(start, end)

  Returns an array of the values contained in the half-open interval [start, end), that is, including the start and excluding the end. For lists and arrays, both terms may be numeric positive or negative indicies. For a list, either term may be a node.

  (Array, List, SortedSet, SortedArray, SortedArraySet)

• splice(start, length, ...values)

  Works as with an array, but for a list, the start may be an index or a node.

  (Array, List, SortedArray, SortedSet, SortedArraySet)

• swap(start, length, values)

  Performs a splice without variadic arguments.

  (Array+, List, SortedArray, SortedSet, SortedArraySet)

• clear()

  Deletes the all values.

  (Array+, Object+, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• sort(compare)

  Sorts a collection in place. The comparator by only be a function. The default comparator coerces unlike types rather than fail to compare.

  (Array)

• sorted(compare, by, order)

  Returns a collection as an array in sorted order. Accepts an optional compare(x, y) function, by(property(x)) function, and order indicator, -1 for descending, 1 for ascending, 0 for stable.

  Instead of a compare function, the comparator can be an object with compare and by functions. The default compare value is Object.compare.

  The by function must be a function that accepts a value from the collection and returns a representative value on which to sort.

  (Array+, List, Set, Map, SortedSet, LruSet, SortedArray, SortedArraySet, FastSet)

• reverse()

  Reverses a collection in place.

  (Array, List)

• reversed()

  Returns a collection of the same type with this collection's contents in reverse order.

  (Array, List)

• concat(...iterables)

  Produces a new collection of the same type containing all the values of itself and the values of any number of other collections. Favors the last of duplicate values. For map-like objects, the given iterables are treated as map-like objects and each successively updates the result. Array is like a map from index to value. List, Set, and SortedSet are like maps from nodes to values.

  (Array, Object+, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• keys()

  Returns an array of the keys.

  (Object, Map, MultiMap, SortedMap, LruMap, SortedArrayMap, FastMap, Dict)

• values()

  Returns an array of the values

  (Object+, Map, MultiMap, SortedMap, LruMap, SortedArrayMap, FastMap, Dict)

• items()

  Returns an array of [key, value] pairs for each item

  (Object+, Map, MultiMap, SortedMap, LruMap, SortedArrayMap, FastMap, Dict)

• reduce(callback(result, value, key, object, depth), basis, thisp):

  (Array, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• reduceRight(callback(result, value, key, object, depth), basis, thisp):

  (Array, List, SortedSet, SortedMap, SortedArray, SortedArraySet, SortedArrayMap)

• forEach(callback(value, key, object, depth), thisp)

  Calls the callback for each value in the collection. The iteration of lists is resilient to changes to the list. Particularly, nodes added after the current node will be visited and nodes added before the current node will be ignored, and no node will be visited twice.

  (Array, Object+, Iterator, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• map(callback(value, key, object, depth), thisp)

  (Array, Object+, Iterator, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• toArray()

  (Array+, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• toObject()

  Converts any collection to an object, treating this collection as a map-like object. Array is like a map from index to value.

  (Array+ Iterator, List, Map, MultiMap, SortedMap, LruMap, SortedArrayMap, FastMap, Dict)

• filter(callback(value, key, object, depth), thisp)

  (Array, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• every(callback(value, key, object, depth), thisp)

  Whether every value passes a given guard. Stops evaluating the guard after the first failure. Iterators stop consuming after the the first failure.

  (Array, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• some(callback(value, key, object, depth), thisp)

  Whether there is a value that passes a given guard. Stops evaluating the guard after the first success. Iterators stop consuming after the first success.

  (Array, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• any()

  Whether any value is truthy.

  (Array+, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• all()

  Whether all values are truthy.

  (Array+, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• min()

  The smallest value. This is fast for sorted collections (logarithic for SortedSet, constant for SortedArray, SortedArraySet, and SortedArrayMap), but slow for everything else (linear).

  (Array+, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• max()

  The largest value. This is fast for sorted collections (logarithic for SortedSet, constant for SortedArray, SortedArraySet, and SortedArrayMap), but slow for everything else (linear).

  (Array+, Iterator, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• one()

  Any single value, or throws an exception if there are no values. This is very fast (constant) for all collections. For a sorted set, the value is not deterministic and depends on what value was most recently accessed.

  (Array+, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• only()

  The one and only value, or throws an exception if there are no values or more than one value.

  (Array+, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• sum()

  (Array+, Iterator, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• average()

  (Array+, Iterator, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• flatten()

  (Array+, Iterator, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• zip(...collections)

  (Array+, Iterator, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• enumrate(zero)

  (Iterator, other collections)

• clone(depth, memo)

  Replicates the collection. Clones the values deeply, to the specified depth, using the memo to resolve reference cycles. (which must the has and set parts of the Map interface, allowing objects for keys) The default depth is infinite and the default memo is a WeakMap.

  Object.clone can replicate object literals inheriting directly from Object.prototype or null, or any object that implements clone on its prototype. Any other object causes clone to throw an exception.

  The clone method on any other objects is not intended to be used directly since they do not necessarily supply a default depth and memo.

  (Array+, Object+, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• constructClone(values)

  Replicates a collection shallowly. This is used by each clone implementation to create a new collection of the same type, with the same options (equals, compare, hash options), but it leaves the job of deeply cloning the values to the more general clone method.

  (Array+, Object+, List, Set, Map, MultiMap, WeakMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• equals(that, equals)

  (Array+, Object+, List, Set, Map, MultiMap, SortedSet, SortedMap, LruSet, LruMap, SortedArray, SortedArraySet, SortedArrayMap, FastSet, FastMap, Dict)

• compare(that)

  (Array+, Object+, List, SortedArray, SortedArraySet)

• iterate()

  Produces an iterator with a next method. You may elect to get richer iterators by wrapping this iterator with an Iterator from the iterator module. Iteration order of lists is resilient to changes to the list.

  (Array+, Iterator, List, Set, SortedSet, LruSet, SortedArray, SortedArraySet, FastSet)

  iterate(start, end)

  Returns an iterator for all values at indicies in the half-open interval [start, end), that is, greater than start, and less than end.

  (Array+)

  iterate(start, end)

  Returns an iterator for all values in the half-open interval [start, end), that is, greater than start, and less than end. The iterator is resilient against changes to the data.

  (SortedSet)

• log(charmap, callback(node, write, writeAbove), log, logger)

  Writes a tree describing the internal state of the data structure to the console.

  charmap is an object that notes which characters to use to draw lines. By default, this is the TreeLog.unicodeRound property from the tree-log module. TreeLog.unicodeSharp and TreeLog.ascii are alternatives. The properties are:

  • intersection: ╋
  • through: ━
  • branchUp: ┻
  • branchDown: ┳
  • fromBelow: ╭
  • fromAbove: ╰
  • fromBoth: ┣
  • strafe: ┃

  callback is a customizable function for rendering each node of the tree. By default, it just writes the value of the node. It accepts the node and a writer functions. The write function produces the line on which the node joins the tree, and each subsequent line. The writeAbove function can write lines before the branch.

  log and loger default to console.log and console. To write the representation to an array instead, they can be array.push and array.

  (SortedSet)

Iterator

• dropWhile(callback(value, index, iterator), thisp)

• takeWhile(callback(value, index, iterator), thisp)

• mapIterator(callback(value, index, iterator))

  Returns an iterator for a mapping on the source values. Values are consumed on demand.

• filterIterator(callback(value, index, iterator))

  Returns an iterator for those values from the source that pass the given guard. Values are consumed on demand.

Iterator utilities

• cycle(iterable, times)

• concat(iterables)

• transpose(iterables)

• zip(...iterables)

  Variadic transpose.

• chain(...iterables)

  Variadic concat.

• range(start, stop, step)

  Iterates from start to stop by step.

• count(start, step)

  Iterates from start by step, indefinitely.

• repeat(value, times)

  Repeats the given value either finite times or indefinitely.

Change Listeners

All collections support change listeners. There are three types of changes. Property changes, map changes, and range changes.

Property Changes

PropertyChanges from the listen/property-changes module can configure listeners for property changes to specific keys of any object.

With the listen/array-changes module required, PropertyChanges can also listen to changes to the length and indexed properties of an array. The only caveat is that watched arrays can only modify their contents with method calls like array.push. All methods of a watched array support change dispatch. In addition, arrays have a set method to make setting the value at a particular index observable.

• PropertyChanges.addOwnPropertyChangeListener(object, key, listener, before)
• PropertyChanges.removeOwnPropertyChangeListener(object, key, listener, before)
• PropertyChanges.dispatchOwnPropertyChange(object, key, value, before)
• PropertyChanges.addBeforeOwnPropertyChangeListener(object, key, listener)
• PropertyChanges.removeBeforeOwnPropertyChangeListener(object, key, listener)
• PropertyChanges.dispatchBeforeOwnPropertyChange(object, key, value)
• PropertyChanges.getOwnPropertyChangeDescriptor(object, key)

All of these functions delegate to methods of the same name if one exists on the object.

• object.addOwnPropertyChangeListener(key, listener, before)
• object.removeOwnPropertyChangeListener(key, listener, before)
• object.dispatchOwnPropertyChange(key, value, before)
• object.addBeforeOwnPropertyChangeListener(key, listener)
• object.removeBeforeOwnPropertyChangeListener(key, listener)
• object.dispatchBeforeOwnPropertyChange(key, value)
• object.getOwnPropertyChangeDescriptor(key)

Additionally, PropertyChanges.prototype can be mixed into other types of objects to support the property change dispatch interface. All collections support this interface.

The listener for a property change receives the arguments value, key, and object, just as a forEach or map callback. The listener may alternately be a delegate object that implements one of these methods:

• listener.handle + key + Change or WillChange
• listener.handleProperty + Change or WillChange
• listener.call

Map Changes

A map change listener receives notifications for the creation, removal, or updates for any item in a map data structure.

With the listen/array-changes module required, Array can also dispatch map changes for the values at each index.

• collection.addMapChangeListener(listener, token, before)
• collection.removeMapChangeListener(listener, token, before)
• collection.dispatchMapChange(key, value, before)
• collection.addBeforeMapChangeListener(listener)
• collection.removeBeforeMapChangeListener(listener)
• collection.dispatchBeforeMapChange(key, value)
• collection.getMapChangeDescriptor()

The listener for a map change receives the value, key, and collection object as arguments, the same pattern as a forEach or map callback. In the after change phase, a value of undefined may indicate that the value was deleted or set to undefined. In the before change phase, a value of undefined may indicate the the value was added or was previously undefined.

The listener may be a delegate object with one of the following methods, in order of precedence:

• listener.handleMap + Change or WillChange
• listener.handleMap + token + Change or WillChange
• listener.call

The listen/map-changes module exports a map changes mixin. The methods of MaxChanges.prototype can be copied to any collection that needs this interface. Its mutation methods will then need to dispatch map changes.

Range Changes

A range change listener receives notifications when a range of values at a particular position is added, removed, or replaced within an ordered collection.

• collection.addRangeChangeListener(listener, token, before)
• collection.removeRangeChangeListener(listener, token, before)
• collection.dispatchRangeChange(plus, minus, index, before)
• collection.addBeforeRangeChangeListener(listener)
• collection.removeBeforeRangeChangeListener(listener)
• collection.dispatchBeforeRangeChange(plus, minus, index)
• collection.getRangeChangeDescriptor()

The listener for a range change is a function that accepts plus, minus, and index arguments. plus and minus are the values that were added or removed at the index. Whatever operation caused these changes is equivalent to:

var minus = collection.splice(index, minus.length, ...plus)

The listener can alternately be a delegate object with one of the following methods in order of precedence:

• handle + token + Range + Change or WillChange
• handleRange + Change or WillChange
• call

The following support range change dispatch:

• Array with require("collections/listen/array-changes")
• SortedSet
• SortedArray
• SortedArraySet

The listen/range-changes module exports a range changes mixin. The methods of RangeChanges.prototype can be copied to any collection that needs this interface. Its mutation methods will need to dispatch the range changes.

All descriptors are objects with the properties changeListeners and willChangeListeners. Both are arrays of listener functions or objects, in the order in which they were added.

Miscellanea

Set and Map

Set and map are like hash tables, but not implemented with a block of memory as they would be in a lower-level language. Most of the work of providing fast insertion and lookup based on a hash is performed by the underlying plain JavaScript object. Each key of the object is a hash string and each value is a List of values with that hash. The inner list resolves collisions. With a good hash method, the use of the list can be avoided.

Sets and maps both have a log function that displays the internal structure of the bucket list in an NPM-style.

┣━┳ 1
┃ ┗━━ {"key":1,"value":"a"}
┣━┳ 2
┃ ┣━━ {"key":2,"value":"c"}
┃ ┗━━ {"key":2,"value":"d"}
┗━┳ 3
  ┗━━ {"key":3,"value":"b"}

Sorted Set and Sorted Map

A binary splay tree is a balanced binary tree that rotates the most frequently used items toward the root such that they can be accessed the most quickly. sorted-set and sorted-map are backed by a splay tree.

All map implementations use an underlying set implementation. Any map can be implemented trivially atop a set by wrapping compare, equals, or hash to operate on the key of an item.

The sorted set has a root node. Each node has a left and right property, which may be null. Nodes are returned by all of the "find" functions, and provided as the key argument to callbacks.

Both sorted-set and sorted-map implement a log function which can produce NPM-style visualizations of the internal state of the sorted tree.

> set.log(SortedSet.ascii)
  .-+ -3
  | '-- -2
.-+ -1
+ 0
| .-- 1
'-+ 2
  '-- 3

> set.log(SortedSet.unicodeRound)
  ╭━┳ -3
  ┃ ╰━━ -2
╭━┻ -1
╋ 0
┃ ╭━┳ 1
┃ ┃ ╰━━ 2
╰━┻ 3

Object and Function Shims

The collection methods on the Object constructor all polymorphically delegate to the corresponding method of any object that implements the method of the same name. So, Object.has can be used to check whether a key exists on an object, or in any collection that implements has. This permits the Object interface to be agnostic of the input type.

Object.empty is an empty object literal.

Object.isObject(value) tests whether it is safe to attempt to access properties of a given value.

Object.is(x, y) compares objects for exact identity and is a good alternative to Object.equals in many collections.

Object.getValueOf(value) safely and idempotently returns the value of an object or value by only calling the valueOf() if the value implements that method.

Object.owns is a shorthand for Object.prototype.hasOwnProperty.call.

Object.can(value, name) checks whether an object implements a method on its prototype chain. An owned function property does not qualify as a method, to aid in distinguishing "static" functions.

Function.noop is returns undefined.

Function.identity returns its first argument.

References

• a SplayTree impementation buried in Fedor Indutny’s super-secret Callgrind. This implementation uses parent references.
• a SplayTree implementation adapted by Paolo Fragomeni from the V8 project and based on the top-down splaying algorithm from "Self-adjusting Binary Search Trees" by Sleator and Tarjan. This does not use or require parent references, so I favored it over Fedor Indutny’s style.
• the interface of ECMAScript harmony simple maps and sets
• a SplayTree implementation from JavaScript data structures mainted by Derrick Burns that supports change-resilient iterators and a comprehensive set of introspection functions.

Future work

Goals

• automate the generation of the method support tables in readme and normalize declaration order
• comprehensive specs and spec coverage tests
• map change dispatch and listeners
• fast list splicing

More possible collections

• arc-set (adaptive replacement cache)
• arc-map
• sorted-order (sorted, can contain duplicates, perhaps backed by splay tree with relaxation on the uniqueness invariant)
• sorted-multi-map (sorted, can contain duplicate entries, backed by sorted-map)
• trie-set
• trie-map
• immutable-* (mutation functions return new objects that largely share the previous version's internal state, some perhaps backed by a hash trie)
• array-heap implementation
• binary-heap implementation