127 lines
4.4 KiB
Markdown
127 lines
4.4 KiB
Markdown
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# Acorn AST walker
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An abstract syntax tree walker for the
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[ESTree](https://github.com/estree/estree) format.
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## Community
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Acorn is open source software released under an
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[MIT license](https://github.com/acornjs/acorn/blob/master/LICENSE).
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You are welcome to
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[report bugs](https://github.com/acornjs/acorn/issues) or create pull
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requests on [github](https://github.com/acornjs/acorn). For questions
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and discussion, please use the
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[Tern discussion forum](https://discuss.ternjs.net).
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## Installation
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The easiest way to install acorn is from [`npm`](https://www.npmjs.com/):
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```sh
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npm install acorn-walk
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```
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Alternately, you can download the source and build acorn yourself:
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```sh
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git clone https://github.com/acornjs/acorn.git
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cd acorn
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npm install
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```
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## Interface
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An algorithm for recursing through a syntax tree is stored as an
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object, with a property for each tree node type holding a function
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that will recurse through such a node. There are several ways to run
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such a walker.
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**simple**`(node, visitors, base, state)` does a 'simple' walk over a
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tree. `node` should be the AST node to walk, and `visitors` an object
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with properties whose names correspond to node types in the [ESTree
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spec](https://github.com/estree/estree). The properties should contain
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functions that will be called with the node object and, if applicable
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the state at that point. The last two arguments are optional. `base`
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is a walker algorithm, and `state` is a start state. The default
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walker will simply visit all statements and expressions and not
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produce a meaningful state. (An example of a use of state is to track
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scope at each point in the tree.)
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```js
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const acorn = require("acorn")
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const walk = require("acorn-walk")
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walk.simple(acorn.parse("let x = 10"), {
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Literal(node) {
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console.log(`Found a literal: ${node.value}`)
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}
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})
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```
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**ancestor**`(node, visitors, base, state)` does a 'simple' walk over
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a tree, building up an array of ancestor nodes (including the current node)
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and passing the array to the callbacks as a third parameter.
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```js
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const acorn = require("acorn")
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const walk = require("acorn-walk")
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walk.ancestor(acorn.parse("foo('hi')"), {
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Literal(_, ancestors) {
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console.log("This literal's ancestors are:", ancestors.map(n => n.type))
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}
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})
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```
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**recursive**`(node, state, functions, base)` does a 'recursive'
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walk, where the walker functions are responsible for continuing the
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walk on the child nodes of their target node. `state` is the start
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state, and `functions` should contain an object that maps node types
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to walker functions. Such functions are called with `(node, state, c)`
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arguments, and can cause the walk to continue on a sub-node by calling
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the `c` argument on it with `(node, state)` arguments. The optional
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`base` argument provides the fallback walker functions for node types
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that aren't handled in the `functions` object. If not given, the
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default walkers will be used.
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**make**`(functions, base)` builds a new walker object by using the
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walker functions in `functions` and filling in the missing ones by
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taking defaults from `base`.
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**full**`(node, callback, base, state)` does a 'full' walk over a
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tree, calling the callback with the arguments (node, state, type) for
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each node
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**fullAncestor**`(node, callback, base, state)` does a 'full' walk
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over a tree, building up an array of ancestor nodes (including the
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current node) and passing the array to the callbacks as a third
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parameter.
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```js
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const acorn = require("acorn")
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const walk = require("acorn-walk")
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walk.full(acorn.parse("1 + 1"), node => {
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console.log(`There's a ${node.type} node at ${node.ch}`)
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})
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```
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**findNodeAt**`(node, start, end, test, base, state)` tries to locate
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a node in a tree at the given start and/or end offsets, which
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satisfies the predicate `test`. `start` and `end` can be either `null`
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(as wildcard) or a number. `test` may be a string (indicating a node
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type) or a function that takes `(nodeType, node)` arguments and
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returns a boolean indicating whether this node is interesting. `base`
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and `state` are optional, and can be used to specify a custom walker.
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Nodes are tested from inner to outer, so if two nodes match the
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boundaries, the inner one will be preferred.
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**findNodeAround**`(node, pos, test, base, state)` is a lot like
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`findNodeAt`, but will match any node that exists 'around' (spanning)
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the given position.
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**findNodeAfter**`(node, pos, test, base, state)` is similar to
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`findNodeAround`, but will match all nodes *after* the given position
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(testing outer nodes before inner nodes).
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