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