Rich-Harris / periscopic

Utility for analyzing scopes belonging to an ESTree-compliant AST

periscopic

Utility for analyzing scopes belonging to an ESTree-compliant AST.

API

import { analyze } from 'periscopic';

const ast = acorn.parse(`
const a = b;
console.log(a);
`);

const { map, globals, scope } = analyze(ast);

• map is a WeakMap<Node, Scope>, where the keys are the nodes of your AST that create a scope
• globals is a Map<string, Node> of all the identifiers that are referenced without being declared anywhere in the program (in this case, b and console)
• scope is the top-level Scope belonging to the program

Scope

Each Scope instance has the following properties:

• scope.block — true if the scope is created by a block statement (i.e. let, const and class are contained to it), false otherwise
• scope.parent — the parent scope object
• scope.declarations — a Map<string, Node> of all the variables declared in this scope, the node value referes to the declaration statement
• scope.initialised_declarations — a Set<string> of all the variables declared and initialised in this scope
• scope.references — a Set<string> of all the names referenced in this scope (or child scopes)

It also has two methods:

• scope.has(name) — returns true if name is declared in this scope or an ancestor scope
• scope.find_owner(name) — returns the scope object in which name is declared (or null if it is not declared)

extract_identifiers and extract_names

This package also exposes utilities for extracting the identifiers contained in a declaration or a function parameter:

import { extract_identifiers, extract_names } from 'periscopic';

const ast = acorn.parse(`
const { a, b: [c, d] = e } = opts;
`);

const lhs = ast.body[0].declarations[0].id;

extract_identifiers(lhs);
/*
[
	{ type: 'Identifier', name: 'a', start: 9, end: 10 },
	{ type: 'Identifier', name: 'c', start: 16, end: 17 },
	{ type: 'Identifier', name: 'd', start: 19, end: 20 }
]
*/

extract_names(lhs);
/*
['a', 'c', 'd']
*/

License

MIT