Recursive descent transformation with visitor

transform.js

#!/usr/bin/env node

/**
 * Depth-first copy with selective transformation.
 * For each of the `Iterable` selected by the selector function, it
 * applies the `visitor` function and continues recursively.
 *
 *
 * @param {object} node the tree structure
 * @param {function} [visitor] the function to apply to selected children
 * @param {function} [childrenSelector] selects an `Iterable` of children
 * @return {object} the new tree
 */
function transform(object, visitor = v => v, childrenSelector = p => true) {
	const copy = Object.create(Object.getPrototypeOf(object));

	for (let p in object) {
		if (!childrenSelector(p)) {
			copy[p] = object[p];
		} else {
			copy[p] = object[p].map(prop =>
				visitor(transform(prop, visitor, childrenSelector))
			);
		}
	}
	return copy;
}

/* Usage: */

const Cardinality = Object.freeze({
	one: 1,
	many: Infinity
});
const entity = {
	label: 'Customer',
	name: 'customer',
	properties: [
		{
			label: 'Given Name',
			name: 'givenName',
			type: 'string',
			cardinality: Cardinality.one
		},
		{
			label: 'Family Name',
			name: 'familyName',
			type: 'string',
			cardinality: Cardinality.one
		},
		{
			label: 'Shipping Address',
			name: 'shippingAddress',
			type: 'object',
			cardinality: Cardinality.one,
			properties: [
				{
					label: 'Street Address',
					name: 'address',
					type: 'string',
					cardinality: Cardinality.one
				},
				{
					label: 'City',
					name: 'city',
					type: 'string',
					cardinality: Cardinality.one
				},
				{
					label: 'State',
					name: 'state',
					type: 'string',
					cardinality: Cardinality.one
				},
				{
					label: 'ZIP Code',
					name: 'zip',
					type: 'string',
					cardinality: Cardinality.one
				}
			]
		}
	]
};

let counter = 0;

function spawn(property) {
	return {
		ref: `${++counter}`,
		context: Object.assign(Object.create(null), property)
	};
}
console.log(
	JSON.stringify(
		transform(entity, spawn, p => 'properties' === p),
		null,
		2
	)
);