froebel/merge.mjs

TypeScript utility library

import clone from "./clone.mjs";

const merge_ = (a, b) => {
  const visited = new Map();
  return mergeItems(a, b, visited);
};

const mergeItems = (a, b, visited) => {
  if (isPrimitive(a) || isPrimitive(b)) return clone(b);
  if (!visited.has(a)) visited.set(a, new Map());
  if (visited.get(a).has(b)) return visited.get(a).get(b);
  let result;

  if (Array.isArray(b)) {
    const clonedA = Array.isArray(a) ? clone(a) : [];
    const clonedB = clone(b);
    result = [...clonedA, ...clonedB];

    for (let i = 0; i < result.length; i++) {
      if (result[i] === clonedA || result[i] === clonedB) result[i] = result;
    }
  } else if (b instanceof Set) {
    result = new Set([...(a instanceof Set ? a : []), ...b]);

    if (result.has(a) || result.has(b)) {
      result.delete(a);
      result.delete(b);
      result.add(result);
    }
  } else if (b instanceof Map) {
    result = new Map([...(a instanceof Map ? a : []), ...b]);
    const keys = [...result.keys()];

    if (keys.includes(a)) {
      result.set(result, result.get(a));
      result.delete(a);
    }

    if (keys.includes(b)) {
      result.set(result, result.get(b));
      result.delete(b);
    }

    for (const [k, v] of result) {
      if (v === a || v === b) result.set(k, result);
    }
  } else {
    const keys = [...new Set([...Object.keys(a), ...Object.keys(b)])];
    result = {};
    visited.get(a).set(b, result);

    for (const key of keys) {
      result[key] = !(key in b) ? clone(a[key]) : !(key in a) ? clone(b[key]) : mergeItems(a[key], b[key], visited);
    }
  }

  visited.get(a).set(b, result);
  return result;
};
/**
 * Recursively merges `A` and `B`. If a property in `A` and `B` is of a
 * different type (i.e. it's not an array, Set, Map, or plain object in both,
 * the value from `B` will be used in the result).
 *
 * If there are self-references in the cloned values, array / Set items, or Map
 * keys or values, they will also be self-referencing in the result.
 */


const merge = merge_;
export default merge;

const isPrimitive = value => typeof value !== "object" || value === null;