135 lines
5.8 KiB
Markdown
135 lines
5.8 KiB
Markdown
<p align="center">
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<img alt="babylon" src="https://raw.githubusercontent.com/babel/logo/master/babylon.png" width="700">
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</p>
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<p align="center">
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Babylon is a JavaScript parser used in <a href="https://github.com/babel/babel">Babel</a>.
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</p>
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<p align="center">
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<a href="https://travis-ci.org/babel/babylon"><img alt="Travis Status" src="https://img.shields.io/travis/babel/babylon/master.svg?style=flat&label=travis"></a>
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<a href="https://codecov.io/gh/babel/babylon"><img alt="Codecov Status" src="https://img.shields.io/codecov/c/github/babel/babylon/master.svg?style=flat"></a>
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</p>
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- The latest ECMAScript version enabled by default (ES2017).
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- Comment attachment.
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- Support for JSX and Flow.
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- Support for experimental language proposals (accepting PRs for anything at least [stage-0](https://github.com/tc39/proposals/blob/master/stage-0-proposals.md)).
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## Credits
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Heavily based on [acorn](https://github.com/marijnh/acorn) and [acorn-jsx](https://github.com/RReverser/acorn-jsx),
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thanks to the awesome work of [@RReverser](https://github.com/RReverser) and [@marijnh](https://github.com/marijnh).
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Significant diversions are expected to occur in the future such as streaming, EBNF definitions, sweet.js integration, interspatial parsing and more.
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## API
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### `babylon.parse(code, [options])`
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### `babylon.parseExpression(code, [options])`
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`parse()` parses the provided `code` as an entire ECMAScript program, while
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`parseExpression()` tries to parse a single Expression with performance in
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mind. When in doubt, use `.parse()`.
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### Options
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- **allowImportExportEverywhere**: By default, `import` and `export`
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declarations can only appear at a program's top level. Setting this
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option to `true` allows them anywhere where a statement is allowed.
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- **allowReturnOutsideFunction**: By default, a return statement at
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the top level raises an error. Set this to `true` to accept such
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code.
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- **allowSuperOutsideMethod**: TODO
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- **sourceType**: Indicate the mode the code should be parsed in. Can be
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either `"script"` or `"module"`.
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- **sourceFilename**: Correlate output AST nodes with their source filename. Useful when generating code and source maps from the ASTs of multiple input files.
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- **startLine**: By default, the first line of code parsed is treated as line 1. You can provide a line number to alternatively start with. Useful for integration with other source tools.
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- **plugins**: Array containing the plugins that you want to enable.
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- **strictMode**: TODO
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### Output
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Babylon generates AST according to [Babel AST format][].
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It is based on [ESTree spec][] with the following deviations:
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> There is now an `estree` plugin which reverts these deviations
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- [Literal][] token is replaced with [StringLiteral][], [NumericLiteral][], [BooleanLiteral][], [NullLiteral][], [RegExpLiteral][]
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- [Property][] token is replaced with [ObjectProperty][] and [ObjectMethod][]
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- [MethodDefinition][] is replaced with [ClassMethod][]
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- [Program][] and [BlockStatement][] contain additional `directives` field with [Directive][] and [DirectiveLiteral][]
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- [ClassMethod][], [ObjectProperty][], and [ObjectMethod][] value property's properties in [FunctionExpression][] is coerced/brought into the main method node.
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AST for JSX code is based on [Facebook JSX AST][] with the addition of one node type:
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- `JSXText`
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[Babel AST format]: https://github.com/babel/babylon/blob/master/ast/spec.md
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[ESTree spec]: https://github.com/estree/estree
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[Literal]: https://github.com/estree/estree/blob/master/es5.md#literal
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[Property]: https://github.com/estree/estree/blob/master/es5.md#property
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[MethodDefinition]: https://github.com/estree/estree/blob/master/es2015.md#methoddefinition
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[StringLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#stringliteral
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[NumericLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#numericliteral
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[BooleanLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#booleanliteral
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[NullLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#nullliteral
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[RegExpLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#regexpliteral
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[ObjectProperty]: https://github.com/babel/babylon/blob/master/ast/spec.md#objectproperty
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[ObjectMethod]: https://github.com/babel/babylon/blob/master/ast/spec.md#objectmethod
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[ClassMethod]: https://github.com/babel/babylon/blob/master/ast/spec.md#classmethod
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[Program]: https://github.com/babel/babylon/blob/master/ast/spec.md#programs
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[BlockStatement]: https://github.com/babel/babylon/blob/master/ast/spec.md#blockstatement
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[Directive]: https://github.com/babel/babylon/blob/master/ast/spec.md#directive
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[DirectiveLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#directiveliteral
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[FunctionExpression]: https://github.com/babel/babylon/blob/master/ast/spec.md#functionexpression
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[Facebook JSX AST]: https://github.com/facebook/jsx/blob/master/AST.md
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### Semver
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Babylon follows semver in most situations. The only thing to note is that some spec-compliancy bug fixes may be released under patch versions.
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For example: We push a fix to early error on something like [#107](https://github.com/babel/babylon/pull/107) - multiple default exports per file. That would be considered a bug fix even though it would cause a build to fail.
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### Example
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```javascript
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require("babylon").parse("code", {
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// parse in strict mode and allow module declarations
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sourceType: "module",
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plugins: [
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// enable jsx and flow syntax
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"jsx",
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"flow"
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]
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});
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```
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### Plugins
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- `estree`
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- `jsx`
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- `flow`
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- `doExpressions`
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- `objectRestSpread`
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- `decorators` (Based on an outdated version of the Decorators proposal. Will be removed in a future version of `Babylon`)
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- `classProperties`
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- `exportExtensions`
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- `asyncGenerators`
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- `functionBind`
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- `functionSent`
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- `dynamicImport`
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- `templateInvalidEscapes`
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