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71 lines
2.0 KiB
Markdown
71 lines
2.0 KiB
Markdown
10 months ago
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# periscopic
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Utility for analyzing scopes belonging to an ESTree-compliant AST.
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## API
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```js
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import { analyze } from 'periscopic';
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const ast = acorn.parse(`
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const a = b;
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console.log(a);
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`);
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const { map, globals, scope } = analyze(ast);
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```
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* `map` is a `WeakMap<Node, Scope>`, where the keys are the nodes of your AST that create a scope
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* `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`)
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* `scope` is the top-level `Scope` belonging to the program
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### Scope
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Each `Scope` instance has the following properties:
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* `scope.block` — true if the scope is created by a block statement (i.e. `let`, `const` and `class` are contained to it), false otherwise
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* `scope.parent` — the parent scope object
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* `scope.declarations` — a `Map<string, Node>` of all the variables declared in this scope, the node value referes to the declaration statement
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* `scope.initialised_declarations` — a `Set<string>` of all the variables declared and initialised in this scope
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* `scope.references` — a `Set<string>` of all the names referenced in this scope (or child scopes)
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It also has two methods:
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* `scope.has(name)` — returns `true` if `name` is declared in this scope or an ancestor scope
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* `scope.find_owner(name)` — returns the scope object in which `name` is declared (or `null` if it is not declared)
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### `extract_identifiers` and `extract_names`
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This package also exposes utilities for extracting the identifiers contained in a declaration or a function parameter:
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```js
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import { extract_identifiers, extract_names } from 'periscopic';
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const ast = acorn.parse(`
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const { a, b: [c, d] = e } = opts;
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`);
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const lhs = ast.body[0].declarations[0].id;
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extract_identifiers(lhs);
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/*
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[
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{ type: 'Identifier', name: 'a', start: 9, end: 10 },
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{ type: 'Identifier', name: 'c', start: 16, end: 17 },
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{ type: 'Identifier', name: 'd', start: 19, end: 20 }
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]
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*/
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extract_names(lhs);
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/*
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['a', 'c', 'd']
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*/
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```
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## License
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[MIT](LICENSE)
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