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Preprocess a tree (encoded as a JSON object) so that given any two nodes in the tree it is possible to determine whether one is the ancestor of the other. Ancestor queries take O(1) time, and the data structure requres O(n) space and preprocessing time.


var preprocess = require("ancestor-of")
//Construct some tree 
var tree = {
  a: {
    x: {},
    y: {}
  b: [ [], [[]] ]
//Construct ancestorOf data structure 
var ancestorOf = preprocess(tree)
//Now we can check ancestor relations on elements of tree: 
var assert = require("assert")
assert.ok(ancestorOf(tree.a, tree.a.x))
assert.ok(!ancestorOf(, tree.a))
assert.ok(!ancestorOf(tree.b, tree.a))
assert.ok(ancestorOf(tree.b, tree.b[1][0]))


npm install ancestor-of


var ancestorOf = require("ancestor-of")(tree[,childrenOf(node)])

Preprocesses tree to answer ancestor queries.

  • tree is the root of a JSON object tree

  • childrenOf(node) is an optional function which returns an array of children of node

    • node is the subtree node

    childrenOf should return an array of all possible children of node

Returns A query which answers ancestor queries


Determine if b is an ancestor of a

  • a is the first node
  • b is the node which is tested to be ancestor of a

Returns true if b is an ancestor of a, otherwise false


Rebuild the data structure if some of the children of tree have changed.


(c) 2014 Mikola Lysenko. MIT License