unist-util-visit-parents

What is unist-util-visit-parents?

The unist-util-visit-parents package is a utility for traversing Unist syntax trees. It allows for visiting nodes, optionally filtered by type, and provides access to parent nodes during traversal. This can be particularly useful for manipulating or inspecting the structure of documents parsed into Unist syntax trees, such as Markdown or HTML parsed by remark or rehype processors.

What are unist-util-visit-parents's main functionalities?

Visiting nodes with access to their parents

This feature allows you to visit all nodes of a specified type ('paragraph' in this example) in a Unist syntax tree, and for each node, you have access to an array of its ancestor nodes. This is useful for context-aware processing or transformations.

visit(tree, 'paragraph', (node, ancestors) => {
  console.log(node);
  console.log(ancestors);
});

Visiting all nodes without filtering

This feature enables visiting all nodes in the syntax tree without filtering by type. Each visited node is accompanied by its ancestors, allowing for comprehensive traversal and manipulation of the tree.

visit(tree, (node, ancestors) => {
  console.log(node);
  console.log(ancestors);
});

Other packages similar to unist-util-visit-parents

unist-util-visit

Similar to unist-util-visit-parents, unist-util-visit allows for traversing Unist trees and applying a function to each visited node. The key difference is that unist-util-visit does not provide access to the ancestors of each node, focusing instead on simpler visitation needs.

unist-util-select

This package provides a way to select nodes in a Unist tree using CSS-like selectors. While it serves a different primary purpose from unist-util-visit-parents, it offers an alternative approach to node selection and manipulation in Unist trees.

README

unist-util-visit-parents

unist utility to visit nodes, with ancestral information.

Install

This package is ESM only: Node 12+ is needed to use it and it must be imported instead of required.

npm:

npm install unist-util-visit-parents

Use

import remark from 'remark'
import {visitParents} from 'unist-util-visit-parents'

var tree = remark.parse('Some _emphasis_, **importance**, and `code`.')

visitParents(tree, 'strong', visitor)

function visitor(node, ancestors) {
  console.log(ancestors)
}

Yields:

[ { type: 'root', children: [ [Object] ] },
  { type: 'paragraph',
    children:
     [ [Object],
       [Object],
       [Object],
       [Object],
       [Object],
       [Object],
       [Object] ] } ]

API

This package exports the following identifiers: visitParents, SKIP, CONTINUE, and EXIT. There is no default export.

visitParents(tree[, test], visitor[, reverse])

Visit nodes (inclusive descendants of tree), with ancestral information. Optionally filtering nodes. Optionally in reverse.

This algorithm performs depth-first tree traversal in preorder (NLR), or if reverse is given, in reverse preorder (NRL).

Walking the tree is an intensive task. Make use of the return values of the visitor when possible. Instead of walking a tree multiple times with different tests, walk it once without a test, and use unist-util-is to check if a node matches a test, and then perform different operations.

Parameters

• tree (Node) — Tree to traverse
• test (Test, optional) — is-compatible test (such as a type)
• visitor (Function) — Function invoked when a node is found that passes test
• reverse (boolean, default: false) — The tree is traversed in preorder (NLR), visiting the node itself, then its head, etc. When reverse is passed, the tree is traversed in reverse preorder (NRL): the node itself is visited, then its tail, etc.

next? = visitor(node, ancestors)

Invoked when a node (matching test, if given) is found.

Visitors are free to transform node. They can also transform the parent of node (the last of ancestors). Replacing node itself, if SKIP is not returned, still causes its descendants to be visited. If adding or removing previous siblings (or next siblings, in case of reverse) of node, visitor should return a new index (number) to specify the sibling to traverse after node is traversed. Adding or removing next siblings of node (or previous siblings, in case of reverse) is handled as expected without needing to return a new index. Removing the children property of an ancestor still results in them being traversed.

Parameters

• node (Node) — Found node
• ancestors (Array.<Node>) — Ancestors of node

Returns

The return value can have the following forms:

• index (number) — Treated as a tuple of [CONTINUE, index]
• action (*) — Treated as a tuple of [action]
• tuple (Array.<*>) — List with one or two values, the first an action, the second and index. Note that passing a tuple only makes sense if the action is SKIP. If the action is EXIT, that action can be returned. If the action is CONTINUE, index can be returned.

action

An action can have the following values:

• EXIT (false) — Stop traversing immediately
• CONTINUE (true) — Continue traversing as normal (same behaviour as not returning anything)
• SKIP ('skip') — Do not traverse this node’s children; continue with the specified index

index

index (number) — Move to the sibling at index next (after node itself is completely traversed). Useful if mutating the tree, such as removing the node the visitor is currently on, or any of its previous siblings (or next siblings, in case of reverse) Results less than 0 or greater than or equal to children.length stop traversing the parent

Related

• unist-util-visit — Like visit-parents, but with one parent
• unist-util-filter — Create a new tree with all nodes that pass a test
• unist-util-map — Create a new tree with all nodes mapped by a given function
• unist-util-flatmap — Create a new tree by mapping (to an array) with the given function
• unist-util-remove — Remove nodes from a tree that pass a test
• unist-util-select — Select nodes with CSS-like selectors

Contribute

See contributing.md in syntax-tree/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.

License

MIT © Titus Wormer