validator for the Shift AST format
Last updated a month ago by shapesecurity .
Apache-2.0 · Repository · Bugs · Original npm · Tarball · package.json
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Shift Validator


We call an AST valid if it represents an ECMAScript program. The Shift AST format was designed to permit the fewest possible conforming ASTs that are not valid. For various reasons, it is impossible to exclude all invalid ASTs. This module distinguishes valid Shift format ASTs from invalid ones.



Note on IfStatements

Most of the ways in which a well-typed AST can fail to be valid are clear from the grammar or spec. One special case is worth calling attention to: an IfStatement with an alternate nested inside the consequent of an IfStatement that lacks an alternate is not valid. No possible source text can produce this AST.


npm install shift-validator


import isValid, {Validator} from "shift-validator";
isValid(myAst); // Boolean
Validator.validate(myAst); // [ValidationError]


  • Open a Github issue with a description of your desired change. If one exists already, leave a message stating that you are working on it with the date you expect it to be complete.
  • Fork this repo, and clone the forked repo.
  • Install dependencies with npm install.
  • Build and test in your environment with npm run build && npm test.
  • Create a feature branch. Make your changes. Add tests.
  • Build and test in your environment with npm run build && npm test.
  • Make a commit that includes the text "fixes #XX" where XX is the Github issue.
  • Open a Pull Request on Github.


Copyright 2014 Shape Security, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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