unist-util-visit

What is unist-util-visit?

The unist-util-visit package is a utility for visiting nodes in a unist syntax tree. It allows for traversal of the tree and application of functions to nodes that match specified conditions. This can be useful for manipulating or inspecting the tree in various ways, such as filtering nodes, applying transformations, or extracting information.

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

Visiting nodes

This feature allows you to visit all nodes in a unist syntax tree that match a specified type. The provided function is called for each matching node. This can be useful for performing operations on specific types of nodes.

visit(tree, 'type', node => { console.log(node) })

Visiting nodes with a test function

This feature allows you to visit all nodes that pass a test implemented by a function. The test function is called with each node, and if it returns true, the node is considered a match. This allows for more complex matching conditions beyond just type.

visit(tree, node => node.value === 'specific value', node => { console.log(node) })

Exiting early

This feature allows you to exit the traversal early by returning `visit.EXIT` from the visitor function. This can be useful for optimizing performance by avoiding unnecessary traversal once a certain condition is met.

visit(tree, 'type', (node, index, parent) => { if (node.value === 'stop') return visit.EXIT })

Other packages similar to unist-util-visit

unist-util-select

This package provides a way to select nodes in a unist syntax tree using CSS-like selectors. It's similar to unist-util-visit in that it allows for node selection, but it uses a different approach based on selectors rather than explicit traversal and testing.

unist-util-filter

unist-util-filter offers functionality to create a new tree by filtering nodes in a unist syntax tree based on a given condition. It's similar to unist-util-visit in its ability to apply conditions to nodes, but instead of visiting nodes, it filters them to produce a new tree.

unist-util-map

This package allows for the creation of a new unist syntax tree by applying a function to every node in an input tree. It's related to unist-util-visit in that it involves applying functions to nodes, but unist-util-map applies the function to all nodes and constructs a new tree based on the results.

README

unist-util-visit

unist utility to walk the tree.

Contents

• What is this?
• When should I use this?
• Install
• Use
• API
  • visit(tree[, test], visitor[, reverse])
  • CONTINUE
  • EXIT
  • SKIP
  • Action
  • ActionTuple
  • BuildVisitor
  • Index
  • Test
  • Visitor
  • VisitorResult
• Types
• Compatibility
• Related
• Contribute
• License

What is this?

This is a very important utility for working with unist as it lets you walk the tree.

When should I use this?

You can use this utility when you want to walk the tree. You can use unist-util-visit-parents if you care about the entire stack of parents.

Install

This package is ESM only. In Node.js (version 16+), install with npm:

npm install unist-util-visit

In Deno with esm.sh:

import {CONTINUE, EXIT, SKIP, visit} from 'https://esm.sh/unist-util-visit@5'

In browsers with esm.sh:

<script type="module">
  import {CONTINUE, EXIT, SKIP, visit} from 'https://esm.sh/unist-util-visit@5?bundle'
</script>

Use

import {fromMarkdown} from 'mdast-util-from-markdown'
import {visit} from 'unist-util-visit'

const tree = fromMarkdown('Some *emphasis*, **strong**, and `code`.')

visit(tree, 'text', function (node, index, parent) {
  console.log([node.value, parent ? parent.type : index])
})

Yields:

[ 'Some ', 'paragraph' ]
[ 'emphasis', 'emphasis' ]
[ ', ', 'paragraph' ]
[ 'strong', 'strong' ]
[ ', and ', 'paragraph' ]
[ '.', 'paragraph' ]

API

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

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

This function works exactly the same as unist-util-visit-parents, but Visitor has a different signature.

CONTINUE

Continue traversing as normal (true).

EXIT

Stop traversing immediately (false).

SKIP

Do not traverse this node’s children ('skip').

Action

Union of the action types (TypeScript type). See Action in unist-util-visit-parents.

ActionTuple

List with an action and an index (TypeScript type). See ActionTuple in unist-util-visit-parents.

BuildVisitor

Build a typed Visitor function from a tree and a test (TypeScript type). See BuildVisitor in unist-util-visit-parents.

Index

Move to the sibling at index next (TypeScript type). See Index in unist-util-visit-parents.

Test

unist-util-is compatible test (TypeScript type).

Visitor

Handle a node (matching test, if given) (TypeScript type).

Visitors are free to transform node. They can also transform parent.

Replacing node itself, if SKIP is not returned, still causes its descendants to be walked (which is a bug).

When adding or removing previous siblings of node (or next siblings, in case of reverse), the Visitor should return a new Index 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 parent still results in them being traversed.

Parameters

• node (Node) — found node
• index (number or undefined) — index of node in parent
• parent (Node or undefined) — parent of node

Returns

What to do next.

An Index is treated as a tuple of [CONTINUE, Index]. An Action is treated as a tuple of [Action].

Passing a tuple back only makes sense if the Action is SKIP. When the Action is EXIT, that action can be returned. When the Action is CONTINUE, Index can be returned.

VisitorResult

Any value that can be returned from a visitor (TypeScript type). See VisitorResult in unist-util-visit-parents.

Types

This package is fully typed with TypeScript. It exports the additional types Action, ActionTuple, BuildVisitor, Index, Test, Visitor, and VisitorResult.

Compatibility

Projects maintained by the unified collective are compatible with maintained versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line, unist-util-visit@^5, compatible with Node.js 16.

Related

• unist-util-visit-parents — walk the tree with a stack of parents
• 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