@mfields/tree

This package exports a single constructor, Tree(), which can be used to create a representation of a general tree. Please see the API Documentation for more information.

Features:

• Immutable API.
• No dependencies.
• Just over 4k minified.
• Written in ES5 - no transpiling necessary.
• Works in all major modern browsers and IE9+.

Installation

npm install @mfields/tree

Usage

As a CommonJS module:

const { Tree } = require('@mfields/tree')

As an ES6 module:

import { Tree } from '@mfields/tree/dist/tree.esm.js'

API Documentation

1. Tree() - Create a new tree.
2. Tree.prototype.add() - Incorporate one tree into another.
3. Tree.prototype.delete() - Remove a node or branch from a tree.
4. Tree.prototype.forEach() - Execute a callback function on each tree.
5. Tree.prototype.get() - Return a reference to a subtree.
6. Tree.prototype.has() - Does this tree contain a tree with a given key?
7. Tree.prototype.isEmpty() - Are all properties of this tree empty?
8. Tree.prototype.sort() - Recursively sort all children.
9. Tree.fromArray() - Create a new tree from a given array of trees.

Tree()

Create a new general tree.

This constructor may be called with or without the new keyword.

Syntax

Tree([config])

Parameter 1: config {Object}

Property	Type	Default	Description
key	Number, String	null	A unique identifier.
parent	Number, String	null	Unique identifier of this tree's parent.
children	Array	[]	Zero or more trees.
*	*	undefined	Zero or more custom properties.

A unique identifier need only be unique within the scope of the tree in which it appears. A tree that contains two children, will always contain 3 unique keys. Likewise, a tree with a size of 549 will contain 549 unique keys.

If a child's parent property is equal to this.id a reference will be saved. In the event that these two values do not match, a derivative instance of the child will be created with its parent value modified to equal this.id.

Custom properties with a value of undefined will be ignored. All other values will be stored as instance properties. All object references will be frozen.

Return value

An instance of Tree will always be returned.

Examples

Empty Trees

In cases where config.key, config.parent and config.children all contain default values and there are no custom properties, an empty tree will be returned. Empty trees are the only trees that have a size of zero.

const empty = Tree()
console.log(empty.isEmpty()) // true

Childless Tree

const childless = Tree({
  key: 66,
  parent: 55,
})

console.log(childless.key) // 66
console.log(childless.parent) // 55
console.log(childless.children) // []
console.log(childless.size) // 1
console.log(childless.isEmpty()) // false

Perfect Binary Tree with Height of 3

const tree = Tree({ key: 1, children: [
  Tree({ key: 2, children: [
    Tree({ key: 4 }),
    Tree({ key: 5 })
  ]}),
  Tree({ key: 3, children: [
    Tree({ key: 6 }),
    Tree({ key: 7 })
  ]})
]})

const tree = Tree({ key: 1, children: [
  Tree({ key: 2, children: [
    Tree({ key: 4 }),
    Tree({ key: 5 })
  ]}),
  Tree({ key: 3, children: [
    Tree({ key: 6 }),
    Tree({ key: 7 })
  ]})
]})

Instance Properties

The following properties have special meaning for each tree instance.

• key {Number|String|null} - This tree's unique identifier.
• parent {Number|String|null} - The key of this tree's parent.
• children {Tree[]} - Zero or more Tree instances.
• size {Number} - A whole number representing the total number of trees (root + all subtrees) contained within this tree.

Tree.prototype.add()

Adds one tree to another as a subtree.

If the descendant's parent exists in this tree, the descendant will be appended to it's parent. If the descendant's parent does not exist in this tree, the descendant will be appended to this tree's root. If the descendant is not an instance of Tree or it is an empty Tree, this will be returned.

Syntax

tree.add([descendant])

Parameters

Name	Type	Default	Description
descendant	Tree	undefined	A tree to add as a subtree.

Return value

A derivative Tree with the descendant added to its parent.

Examples

Add one tree to another

var a = Tree({ key: 22 })
var b = Tree({ key: 33 })
var c = a.add(b)

console.log(a.size) // 1
console.log(b.size) // 1
console.log(c.size) // 2

Tree.prototype.delete()

Remove a subtree.

Syntax

tree.delete(key)

Parameters

Name	Type	Description
key	Number, String	The unique identifier of a subtree to remove.

Return value

A derivative tree without the subtree indicated by the key parameter. In cases where the key of the root tree is provided as the key parameter, an empty tree will be returned.

Tree.prototype.forEach()

Execute a given function once for each tree (root + all subtrees).

This method works in a very similar fashion to Array.prototype.forEach().

Syntax

tree.forEach(callback, [thisArg])

Parameters

Name	Type	Default	Description
callback	Function	undefined	Function to execute on each tree.
thisArg	Object	undefined	Value to use as this for each iteration.

Return value

The return value of this method is undefined.

Tree.prototype.get()

Get a reference to a subtree by key.

Syntax

tree.get(key)

Parameters

Name	Type	Default	Description
key	Number, String	undefined	The unique identifier of the tree to return.

Return value

A value of Tree will be returned if the requested tree can be found as a descendant. If not, null will be returned.

Tree.prototype.has()

Does this tree have a tree with a given key?

Syntax

tree.has(key)

Parameters

Name	Type	Default	Description
key	Number, String	undefined	The unique identifier of the tree in question.

Return value

Boolean - true if the requested tree was found; false otherwise. This method will consider the root tree as well as all of its subtrees.

Tree.prototype.isEmpty()

Is this tree empty?

An empty tree has the following properties:

key: null
parent: null
children: []
size: 0

Syntax

tree.isEmpty()

Parameters

This method recognizes no properties.

Return value

Boolean - A value of true will be returned if the tree is empty; false will be returned otherwise.

Tree.prototype.sort()

Recursively sort all subtrees.

Syntax

tree.sort([options])

Parameter 1: options {Object} optional

Property	Type	Default	Description
comparator	Function	Function	Custom sort function. optional
deep	Boolean	true	Should all trees be sorted? optional

When options.comparator is not provided, this method will sort subtrees by key in ascending order.

When options.deep is true all of its subtrees will be sorted. When false only the root tree's children will be sorted.

Return value

Returns a derivative instance of Tree with subtrees sorted.

Tree.fromArray()

Assemble a list of trees into a single tree by nesting instance based on their parent/child relationship.

Syntax

Tree.fromArray(trees, [options])

Parameter 1: trees {Array}

A list of Tree instances from which to build a new tree.

Parameter 2:

Property	Type	Default	Description
height	Number	0	The height that the generated tree is allowed grow to. If defined, this value must be a integer greater than 1.
comparator	Function	by key	Optional sort function.

Return value

Tree - A composite tree containing all trees represented in the trees parameter.

Examples

Default Usage

Create a new tree of height 3 from a flat list.

var tree = Tree.fromArray([
  Tree({ key:  1, parent:  0 }),
  Tree({ key:  2, parent:  1 }),
  Tree({ key:  3, parent:  2 })
])

console.log(tree.size) // 3
console.log(tree.children[0] ) // { key: 2 }
console.log(tree.children[0].children[0] ) // { key: 1 }

Orphan collection.

Trees will be appended to the root tree if their parent does not exist in the list. If no root exists one will be created from an empty tree.

var tree = Tree.fromArray([
  Tree({ key: 2, parent: 5 }),
  Tree({ key: 3, parent: 6 }),
  Tree({ key: 4, parent: 7 }),
])

console.log(tree.size) // 4
console.log(tree.children[0].key) // 2
console.log(tree.children[1].key) // 3
console.log(tree.children[2].key) // 4

Height reduction.

var trees = [
  Tree({ key: 1, parent: 0 }),
  Tree({ key: 2, parent: 1 }),
  Tree({ key: 3, parent: 2 }),
  Tree({ key: 4, parent: 3 }),
  Tree({ key: 5, parent: 4 }),
]

var tree2 = Tree.fromArray(trees, { height: 2 })

console.log(tree2.size) // 5
console.log(tree2.children.length) // 4

var tree3 = Tree.fromArray(trees, { height: 3 })

console.log(tree3.size) // 5
console.log(tree3.children.length) // 1
console.log(tree3.children[0].children.length) // 3

var tree4 = Tree.fromArray(trees, { height: 4 })

console.log(tree4.size) // 5
console.log(tree4.children.length) // 1
console.log(tree4.children[0].children.length) // 1
console.log(tree4.children[0].children[0].children.length) // 2