ASTy

Abstract Syntax Tree (AST) Data Structure

Installation

$ npm install asty

About

ASTy is a Abstract Syntax Tree (AST) Data Structure library for JavaScript, i.e., it provides a hierarchical data structure for holding the syntax abstraction of an arbitrary formal language. It is usually used in combination with a parser generator like PEG.js (and then especially with its utility class PEGUtil) to carry the results of the parsing step and to provide the vehicle for further processing those results.

Usage

ASTy provides a context (ASTYCtx below) for the creation of AST node (ASTYNode below). The tree of AST nodes is formed by linking child AST nodes into a parent AST node. The ASTy API, here assumed to be exposed through the variable ASTY, provides the following methods (in a notation somewhat resembling TypeScript type definitions):

ASTy Context (ASTYCtx)

• new ASTY(): ASTYCtx:
  Create a new instance of the ASTy context. It internally captures the prototype (ASTYNode) of the AST nodes to be created.

• ASTYCtx#version(): { major: Number, minor: Number, micro: Number, date: Number }:
  Return the ASTy version detals. The date is in numeric format YYYYMMDD.

• ASTYCtx#extend(object: { [methodName: String]: [methodFunc: Function] }): ASTYCtx:
  Extend the internal ASTYNode prototype with additional methods which are then available on each ASTYNode instance when created with ASTYCtx#create. This should be used by ASTy extension modules only.

• ASTYCtx#create(type: String, attrs?: {[name: String]: [value: Object]}, childs?: ASTY[]): ASTYNode:
  Create a new ASTYNode instance of type and optionally already set attributes and add child nodes.

• ASTYCtx#isA(object: Object): Boolean:
  Check whether object is an ASTYNode instance.

• static ASTYCtx::serialize(node: ASTYNode): String:
  Serializes (formats) ASTy nodes to JSON string. Use this for exporting an AST.

• static ASTYCtx::unserialize(json: String): ASTYNode:
  Unserializes (parses) JSON string to ASTy nodes. Use this for importing an AST.

ASTy Node (ASTYNode)

• ASTYNode#create(type: String, attrs?: {[name: String]: [value: Object]}, childs?: ASTY[]): ASTYNode:
  Create a new ASTYNode instance of type and optionally already set attributes and add child nodes.

• ASTYNode#merge(node: Node, takePos?: Boolean, attrMap?: {[from: String]: [to: (String|null)})): ASTYNode:
  Merge attributes, childs and optionally the position of a node. The attributes can be renamed or skipped (if mapped onto null).

• ASTYNode#type(type: String): Boolean:
  ASTYNode#type(): String:
  Set or get type of node.

• ASTYNode#pos(line: Number, column: Number, offset: Number): ASTYNode:
  ASTYNode#pos(): { line: Number, column: Number, offset: Number }:
  Set or get the position for the node.

• ASTYNode#set(name: String, value: Object): ASTYNode:
  ASTYNode#set({ [String]: Object }): ASTYNode:
  Set a single attribute name to value or set multiple attributes to their corresponding value.

• ASTYNode#unset(name: String): ASTYNode:
  ASTYNode#unset(names: String[]): ASTYNode:
  Unset a single attribute name or unset multiple attributes.

• ASTYNode#set({ [name: String]: [value: Object] }): ASTYNode:
  Set multiple attributes, each consisting of name and value pairs.

• ASTYNode#get(name: String): Object:
  ASTYNode#get(names: String[]): Object[]:
  Get value of a particular attribute name, or get array of values corresponding to each name in names.

• ASTYNode#attrs(): String[]:
  Get names of all node attributes.

• ASTYNode#nth(): Number:
  Get position among sibling nodes in parent's child node list. The positions start at 0.

• ASTYNode#ins(pos: Number, childs: ASTYNode[]): ASTYNode:
  Add one or more childs to a node, at a fixed position pos. The array childs can either contain ASTYNode objects or even arrays of ASTYNode objects. If pos is negative it counts from the end of child list, with -1 the position after the last existing child.

• ASTYNode#add(childs: ASTYNode[]): ASTYNode:
  Add one or more childs to a node, at the end of the child list. The array childs can either contain ASTYNode objects or even arrays of ASTYNode objects.

• ASTYNode#del(childs: ASTYNode[]): ASTYNode:
  Delete one or more childs from a node.

• ASTYNode#childs(begin?: Number, end?: Number): ASTYNode[]:
  Get a nodes list of all or some childs. The begin and end parameters are passed-through to Array::slice. If the range from begin to end is out of range, an empty array is returned.

• ASTYNode#child(pos: Number): ASTYNode:
  Get a particular child node. If pos is out of range, null is returned.

• ASTYNode#parent(): ASTYNode:
  Get parent node.

• ASTYNode#walk(callback: (node: ASTYNode, depth: Number, parent: ASTYNode, when: String) => Void, when?: String): ASTYNode:
  Recursively walk the AST starting at this node (at depth 0). For each visited node the callback function is called with the current node, the current node's tree depth, the current node's parent node and the current walking situation. By default (and if when is either downward or both), the callback is called in the downward phase, i.e., before(!) all child nodes will be visited, and with when set to downward. If when is set to upward or both, the callback is called in the upward phase, i.e., after(!) all child nodes were visited, and with when set to upward.

• ASTYNode#dump(maxDepth?: Number, colorize?: (type: String, text: String) => String, unicode?: Boolean): String:
  Returns a textual dump of the AST starting at the current node. By default maxDepth is Infinity and this way the whole AST below the current node is dumped. If maxDepth is 0 only the current node is dumped. If maxDepth is 1 the current node and all its direct child nodes are dumped. The parameter colorize is an optional callback function, intended to colorize the output text fragments according to their type. The following type strings are supported: tree, type, parenthesis, comma, key, colon, value, position, bracket, line, slash, and column. If unicode is set to false, ASCII substitution characters are used for the tree structure.

• ASTYNode#serialize(): String:
  Recursively serializes the AST node to JSON. Use this for exporting.

Implementation Notice

Although ASTy is written in ECMAScript 2018, it is transpiled to older environments and this way runs in really all current (as of 2018) JavaScript environments, of course.

Additionally, there are two transpilation results: first, there is a compressed asty.browser.js for Browser environments. Second, there is an uncompressed asty.node.js for Node.js environments.

Alternatives

A few decent alternatives to ASTy exist:

• UniST and UniST Builder
• estree
• AST-Types

License

Copyright (c) 2014-2021 Dr. Ralf S. Engelschall (http://engelschall.com/)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.