froebel/clone.mjs

TypeScript utility library

/**
 * Returns a copied version of `value`.
 *
 * If `value` is primitive, returns `value`.
 * Otherwise, properties of `value` are copied recursively. Only `value`'s own
 * enumerable properties are cloned. Arrays are cloned by mapping over their
 * elements.
 *
 * If a path in `value` references itself or a parent path, then in the
 * resulting object that path will also reference the path it referenced in the
 * original object (but now in the resuling object instead of the original).
 */
const clone = globalThis.structuredClone ?? cloneFallback;
export default clone;

function cloneFallback(value) {
  const map = new Map();
  const replacers = [];

  const cloned = _clone(value, map, replacers, undefined);

  for (const f of replacers) f();

  return cloned;
}

function _clone(v, visited, replacers, replace) {
  if (typeof v !== "object" || v === null) return v;
  if (visited.has(v)) return replace(v);
  visited.set(v, 0);

  const cloneNext = (v, r) => _clone(v, visited, replacers, v => replacers.push(() => r(v)));

  const cloned = Array.isArray(v) ? v.map((e, i) => cloneNext(e, v => cloned[i] = visited.get(v))) : Object.fromEntries(Object.entries(v).map(([k, e]) => [k, cloneNext(e, v => cloned[k] = visited.get(v))]));
  visited.set(v, cloned);
  return cloned;
}