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The ESTree Spec

Once upon a time, an unsuspecting Mozilla engineer created an API in Firefox that exposed the SpiderMonkey engine's JavaScript parser as a JavaScript API. Said engineer documented the format it produced, 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

extend interface Program {
    sourceType: "script" | "module";
    body: [ Statement | ImportOrExportDeclaration ];
}

ESTree Steering Committee

Copyright and License

Copyright Mozilla Contributors and ESTree Contributors.

Licensed under Creative Commons Sharealike.

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)
  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)
  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)
  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)

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 (Babel), Kyle Simpson (@getify), Mike Sherov (Esprima), Ariya Hidayat (Esprima), Adrian Heine (Acorn), Dave Herman (SpiderMonkey), Michael Ficarra (@michaelficarra).