SWC-to-babel

Convert SWC JavaScript AST to Babel AST.

To use SWC parser with babel tools like:

• @babel/traverse
• @babel/types
• etc...

The thing is @babel/parser has a a little differences with swc standard:

• File node exists;
• Program instead of Module;
• loc with line and column instead of span;
• StringLiteral has no kind an hasEscape;
• Identifier has no optional and uses name instead of value;
• BlockStatement has body instead of stmts;
• VariableDeclarator has no optional and definite;
• CallExpression has no typeArguments, spread and expression properties in arguments;
• TemplateElement has value field with raw and cooked;
• TypeScript ast nodes has prefix TS instead of Ts;
• ExportNamedDeclaration instead of ExportDeclaration;
• ExportDefaultDeclaration instead of ExportDefaultExpression;
• VariableDeclaration has no declare field;
• Has no ParenthesisExpression;
• ClassDeclaration and ClassExpression uses id instead of identifier, has ClassBody;
• ClassMethod uses static instead of isStatic;
• MemberExpression has computed property instead of Computed node in property field;
• NewExpression has no untyped node with a spread property in arguments, always has arguments field, instead of null when absent;
• ArrayExpression has no untyped node with a spread property in elements;
• Function has no typeParameters;
• TSTypeReference has no typeParams field;
• TSTypeOperator has operator instead of op;
• TSTypeParameter has a field name which is string instead of Identifier;
• FunctionDeclaration instead of FunctionExpression with identifier field;
• ImportDeclaration has importKind instead of typeOnly and attributes fields;
• ObjectProperty instead of KeyValueProperty, KeyValuePatternProperty and AssignmentPatternProperty;
• ExportNamedDeclaration has exportKind, specifiers fields;
• ExportSpecifier has local which is never null instead of orig;
• ExportDefaultDeclaration has declaration instead of decl;
• TSAnyKeyword instead of TSKeywordType;
• TSAsExpression instead of TsConstAssertion;
• ObjectMethod with kind: get instead of GetterProperty;
• ObjectMethod with kind: set instead of SetterProperty;
• TSMappedType typeParameter.constraint, instead of typeParameter;
• etc...

swc-to-babel aims to smooth this differences.

Install

npm i swc-to-babel

Example

import swc from '@swc/core';
import toBabel from 'swc-to-babel';
import traverse from 'babel/traverse';

const ast = toBabel(swc.parseSync(`
    const f = ({a}) => a;
`));

traverse({
    ObjectProperty(path) {
        console.log(path.value.name);
        // output
        'a';
    },
});

API reference

/**
 * Convert an SWC ast to a babel ast
 * @param ast {Module} SWC ast
 * @param {string} [src=""] Source code
 * @returns {ParseResult<File>} Babel ast
 */
export default function toBabel(ast: Module, src?: string): ParseResult<File>;

License

MIT