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])` ### 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. - **plugins**: Array containing the plugins that you want to enable. ### Output Babylon generates AST according to [Babel AST format][]. It is based on [ESTree spec][] with the following 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 - `jsx` - `flow` - `doExpressions` - `objectRestSpread` - `decorators` - `classProperties` - `exportExtensions` - `asyncGenerators` - `functionBind` - `functionSent` - `dynamicImport`