node_modules/unist-util-is/index.js

'use strict'

var convert = require('./convert')

module.exports = is

is.convert = convert

// Assert if `test` passes for `node`.
// When a `parent` node is known the `index` of node should also be given.
function is(node, test, index, parent, context) {
  var check = convert(test)

  if (
    index != null &&
    (typeof index !== 'number' || index < 0 || index === Infinity)
  ) {
    throw new Error('Expected positive finite index')
  }

  if (parent != null && (!is(parent) || !parent.children)) {
    throw new Error('Expected parent node')
  }

  if ((parent == null) !== (index == null)) {
    throw new Error('Expected both parent and index')
  }

  return node && node.type && typeof node.type === 'string'
    ? Boolean(check.call(context, node, index, parent))
    : false
}