26809e8ce7
* Property variance type annotations for Flow plugin Non-method properties and indexers of object types, declare class, and interfaces can be "positive" or "negative." Class fields, but again not methods, can also have variance. This PR generalizes the variance annotations for type parameters into a new node type, and reuses that node for those properties. The code for object types is reused for interfaces and declare classes. The changes there are straightfoward. The code for class fields is reused for object literals, which do not support variance annotations (currently). This code is a bit sketchy, because we always parse variance annotations in the `parsePropertyName` extension, then error in a the subsequent parse phase for object literals (`parseObjPropValue`) or class methods (`parseClassMethod`). * Remove bogus unreachable code, clarify variance parsing conditional * Don't use a new node type for variance annotations Adding a new node type, specifically changing the TypeParameter node's variance property to be node-valued, is a breaking change. We might choose to make this breaking change in a later version. * s/start/variancePos
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.
Credits
Heavily based on acorn and acorn-jsx, thanks to the awesome work of @RReverser and @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,
importandexportdeclarations can only appear at a program's top level. Setting this option totrueallows them anywhere where a statement is allowed. -
allowReturnOutsideFunction: By default, a return statement at the top level raises an error. Set this to
trueto 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
directivesfield 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
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 - multiple default exports per file. That would be considered a bug fix even though it would cause a build to fail.
Example
require("babylon").parse("code", {
// parse in strict mode and allow module declarations
sourceType: "module",
plugins: [
// enable jsx and flow syntax
"jsx",
"flow"
]
});
Plugins
jsxflowdoExpressionsobjectRestSpreaddecoratorsclassPropertiesexportExtensionsasyncGeneratorsfunctionBindfunctionSentdynamicImport