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https://github.com/estree/estree

The ESTree Spec
https://github.com/estree/estree

ast estree javascript parsing specification

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The ESTree Spec

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# The ESTree Spec



Once upon a time, an [unsuspecting Mozilla engineer](http://calculist.org) created an API in Firefox that exposed the SpiderMonkey engine's JavaScript parser as a JavaScript API. Said engineer [documented the format it produced](https://web.archive.org/web/20210314002546/https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Parser_API), and this format caught on as a lingua franca for tools that manipulate JavaScript source code.



Meanwhile JavaScript is evolving. This site will serve as a community standard for people involved in building and using these tools to help evolve this format to keep up with the evolution of the JavaScript language.



# AST Descriptor Syntax



The spec uses a custom syntax to describe its structures.  For example, at the

time of writing, 'es2015.md' contained a description of `Program` as seen below



```js

extend interface Program {

    sourceType: "script" | "module";

    body: [ Statement | ImportOrExportDeclaration ];

}

```



# ESTree Steering Committee



* [Nicholas C. Zakas](https://github.com/nzakas) ([ESLint](https://github.com/eslint))

* [Ingvar Stepanyan](https://github.com/rreverser) ([Acorn](https://github.com/acornjs/acorn))

* [Junliang Huang](https://github.com/JLHwung) ([Babel](https://github.com/babel))



# Copyright and License



Copyright Mozilla Contributors and ESTree Contributors.



Licensed under [Creative Commons Sharealike](https://creativecommons.org/licenses/by-sa/2.5/).



# Philosophy



Suggested additions and modifications must follow these guidelines:



1. **Backwards compatible:** Non-additive modifications to existing constructs will not be considered unless immense support is in favor of such changes. ([eg. #65](https://github.com/estree/estree/issues/65))

2. **Contextless:** Nodes should not retain any information about their parent. ie. a `FunctionExpression` should not be aware of if it's a concise method. (eg. [#5](https://github.com/estree/estree/issues/5))

3. **Unique:** Information should not be duplicated. ie. a `kind` property should not be present on `Literal` if the type can be discerned from the `value`. (eg. [#61](https://github.com/estree/estree/issues/61))

4. **Extensible:** New nodes should be specced to easily allow future spec additions. This means expanding the coverage of node types. ie. `MetaProperty` over `NewTarget` to cover future meta properties. (eg. [#32](https://github.com/estree/estree/pull/32))



# Acknowledgements



ESTree has benefited from the contributions of many people over the years. We'd like to thank these folks for their significant contributions to this project:



[Sebastian McKenzie](https://github.com/sebmck) ([Babel](https://github.com/babel/babel)), Kyle Simpson ([@getify](https://github.com/getify)), [Mike Sherov](https://github.com/mikesherov) ([Esprima](https://github.com/jquery/esprima)), [Ariya Hidayat](https://github.com/ariya) ([Esprima](https://github.com/jquery/esprima)), [Adrian Heine](https://github.com/adrianheine) ([Acorn](https://github.com/acornjs/acorn)), [Dave Herman](https://github.com/dherman) (SpiderMonkey), Michael Ficarra ([@michaelficarra](https://github.com/michaelficarra)).