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.
unist-util-visit
unist utility to walk the tree.
Contents
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 nodeindex
(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
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