Acorn AST walker

An abstract syntax tree walker for the
ESTree format.

Community

Acorn is open source software released under an
MIT license.

You are welcome to
report bugs or create pull
requests on github.

Installation

The easiest way to install acorn is from npm:

 npm install acorn-walk

Alternately, you can download the source and build acorn yourself:

 git clone https://github.com/acornjs/acorn.git
cd acorn
npm install

Interface

An algorithm for recursing through a syntax tree is stored as an
object, with a property for each tree node type holding a function
that will recurse through such a node. There are several ways to run
such a walker.

simple(node, visitors, base, state) does a 'simple' walk over a
tree. node should be the AST node to walk, and visitors an object
with properties whose names correspond to node types in the ESTree
spec. The properties should contain
functions that will be called with the node object and, if applicable
the state at that point. The last two arguments are optional. base
is a walker algorithm, and state is a start state. The default
walker will simply visit all statements and expressions and not
produce a meaningful state. (An example of a use of state is to track
scope at each point in the tree.)

 const acorn = require("acorn")
const walk = require("acorn-walk")

walk.simple(acorn.parse("let x = 10"), {
  Literal(node) {
    console.log(`Found a literal: ${node.value}`)
  }
})

ancestor(node, visitors, base, state) does a 'simple' walk over
a tree, building up an array of ancestor nodes (including the current node)
and passing the array to the callbacks as a third parameter.

 const acorn = require("acorn")
const walk = require("acorn-walk")

walk.ancestor(acorn.parse("foo('hi')"), {
  Literal(_node, _state, ancestors) {
    console.log("This literal's ancestors are:", ancestors.map(n => n.type))
  }
})

recursive(node, state, functions, base) does a 'recursive'
walk, where the walker functions are responsible for continuing the
walk on the child nodes of their target node. state is the start
state, and functions should contain an object that maps node types
to walker functions. Such functions are called with (node, state, c)
arguments, and can cause the walk to continue on a sub-node by calling
the c argument on it with (node, state) arguments. The optional
base argument provides the fallback walker functions for node types
that aren't handled in the functions object. If not given, the
default walkers will be used.

make(functions, base) builds a new walker object by using the
walker functions in functions and filling in the missing ones by
taking defaults from base.

full(node, callback, base, state) does a 'full' walk over a
tree, calling the callback with the arguments (node, state, type) for
each node

fullAncestor(node, callback, base, state) does a 'full' walk
over a tree, building up an array of ancestor nodes (including the
current node) and passing the array to the callbacks as a third
parameter.

 const acorn = require("acorn")
const walk = require("acorn-walk")

walk.full(acorn.parse("1 + 1"), node => {
  console.log(`There's a ${node.type} node at ${node.ch}`)
})

findNodeAt(node, start, end, test, base, state) tries to locate
a node in a tree at the given start and/or end offsets, which
satisfies the predicate test. start and end can be either null
(as wildcard) or a number. test may be a string (indicating a node
type) or a function that takes (nodeType, node) arguments and
returns a boolean indicating whether this node is interesting. base
and state are optional, and can be used to specify a custom walker.
Nodes are tested from inner to outer, so if two nodes match the
boundaries, the inner one will be preferred.

findNodeAround(node, pos, test, base, state) is a lot like
findNodeAt, but will match any node that exists 'around' (spanning)
the given position.

findNodeAfter(node, pos, test, base, state) is similar to
findNodeAround, but will match all nodes after the given position
(testing outer nodes before inner nodes).