flAST – FLat Abstract Syntax Tree

Flatten an Abstract Syntax Tree by placing all of the nodes in a single flat array.

Features

  • Keeps all relations between parent and child nodes.
  • Tracks scope and connects each declaration to its references. See eslint-scope for more info on the scopes used.
  • Adds a unique id to each node to simplify tracking and understanding relations between nodes.
  • Arborist – marks nodes for replacement or deletion and applies all changes in a single iteration over the tree.

Installation

npm install flast

Expected Data Structure

Example of how a flat AST would look like.

Input code: console.log('flAST');. Output object:

const tree = [
	{
		type: 'program',
		start: 0,
		end: 21,
		range: [0, 21],
		body: [
			'<ref to nodeId#2>'
		],
		sourceType: 'script',
		comments: [],
		nodeId: 0,
		src: "console.log('flAST');",
		childNodes: [
			'<ref to nodeId#1>'
		],
		parentNode: null,
		scope: '<GlobalScope scopeId#0>'
	},
	{
		type: 'ExpressionStatement',
		start: 0,
		end: 21,
		range: [0, 21],
		expression: '<ref to nodeId#2>',
		nodeId: 1,
		src: "console.log('flAST');",
		childNodes: [
			'<ref to nodeId#2>'
		],
		parentNode: '<ref to nodeId#0>',
		scope: '<GlobalScope scopeId#0>'
	},
	{
		type: 'CallExpression',
		start: 0,
		end: 20,
		range: [0, 20],
		callee: '<ref to nodeId#3>',
		arguments: [
			'<ref to nodeId#6>'
		],
		optional: false,
		nodeId: 2,
		src: "console.log('flAST')",
		childNodes: [
			'<ref to nodeId#3>',
			'<ref to nodeId#6>'
		],
		parentNode: '<ref to nodeId#1>',
		scope: '<GlobalScope scopeId#0>'
	},
	{
		type: 'MemberExpression',
		start: 0,
		end: 11,
		range: [0, 11],
		object: '<ref to nodeId#4>',
		property: '<ref to nodeId#5>',
		computed: false,
		optional: false,
		nodeId: 3,
		src: 'console.log',
		childNodes: [
			'<ref to nodeId#4>',
			'<ref to nodeId#5>'
		],
		parentNode: '<ref to nodeId#2>',
		scope: '<GlobalScope scopeId#0>'
	},
	{
		type: 'Identifier',
		start: 0,
		end: 7,
		range: [0, 7],
		name: 'console',
		nodeId: 4,
		src: 'console',
		childNodes: [],
		parentNode: '<ref to nodeId#3>',
		scope: '<GlobalScope scopeId#0>'
	},
	{
		type: 'Identifier',
		start: 8,
		end: 11,
		range: [8, 11],
		name: 'log',
		nodeId: 5,
		src: 'log',
		childNodes: [],
		parentNode: '<ref to nodeId#3>',
		scope: '<GlobalScope scopeId#0>'
	},
	{
		type: 'Literal',
		start: 12,
		end: 19,
		range: [12, 19],
		value: "flAST",
		raw: "'flAST'",
		nodeId: 6,
		src: "'flAST'",
		childNodes: [],
		parentNode: '<ref to nodeId#2>',
		scope: '<GlobalScope scopeId#0>'
	}
];

Usage

flAST

const {generateFlatAST, generateCode} = require('flast');
const ast = generateFlatAST(`console.log('flAST'`);
const reconstructedCode = generateCode(ast[0]); // rebuild from root node

generateFlatAST Options

const generateFlatASTDefaultOptions = {
	detailed: true,   // If false, include only original node without any further details
	includeSrc: true, // If false, do not include node src. Only available when `detailed` option is true
};

generateCode Options

See Espree’s documentation for more information

const generateCodeDefaultOptions = {
	format: {
		indent: {
			style: '  ',
			adjustMultilineComment: true,
		},
		quotes: 'auto',
		escapeless: true,
		compact: false,
	},
	comment: true,
};

Arborist

const {generateFlatAST, generateCode, Arborist} = require('flast');
const ast = generateFlatAST(`console.log('Hello' + ' ' + 'there!');`);
const replacements = {
  'Hello': 'General',
  'there!': 'Kenobi',
};
const arborist = new Arborist(ast);
// Mark all relevant nodes for replacement.
ast.filter(n => n.type === 'Literal' && replacements[n.value]).forEach(n => arborist.markNode(n, {
  type: 'Literal',
  value: replacements[n.value],
  raw: `'${replacements[n.value]}'`,
}));
const numberOfChangesMade = arborist.applyChanges();
console.log(generateCode(arborist.ast[0]));  // console.log('General' + ' ' + 'Kenobi');

The Arborist can be called with an extra argument – logFunc – which can be used to log inside the arborist.

Contribution

To contribute to this project see our contribution guide

GitHub

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