[kitten]

Summary

When applied, these changes let the native side filter visitor matches before preparing callback data or dispatching to JS, reducing unnecessary callbacks on expensive plugins.

defineVisitor now also accepts a selector object with:

• route and where to select nodes by type and fields.
• parent to constrain the immediate AST parent.
• children to constrain named child roles, with optional list index.

This is backwards-compatible and filed as a patch instead, since we're still in 0. releases.

Examples

Conditionals combine in an AND logic and are:

Filter by fields:

defineVisitor(
  { route: 'Identifier', where: { name: { equals: 'exports' } } },
  { fields: ['name'] },
  path => console.log(path.node.name),
);

Match an immediate parent:

defineVisitor(
  { route: 'VariableDeclaration', parent: { route: 'Program' } },
  { fields: ['kind'] },
  path => console.log(path.node.kind),
);

Match a named child, while delivering the root node:

defineVisitor(
  {
    route: 'AssignmentExpression',
    children: {
      left: {
        route: 'Identifier',
        where: { name: { equals: 'exports' }, global: { equals: true } },
      },
    },
  },
  {},
  (_path, state: { hasCjsExports: boolean }) => {
    state.hasCjsExports = true;
  },
);

Match a particular list position:

defineVisitor(
  {
    route: 'CallExpression',
    children: {
      arguments: {
        route: 'Identifier',
        index: 0,
        where: { name: { equals: 'exports' } },
      },
    },
  },
  {},
  () => console.log('First argument is exports'),
);