Deep Clone II

hardcodingJavaScriptObjectsRecursion~45 min

Asked at Google, Meta, Stripe

Overview

Implement deepClone(value) handling:

Circular references
Date, RegExp, Map, Set
Nested objects and arrays

Constraints

Must not enter infinite loops on circular refs
Preserve prototypes of built-in types

Examples

const obj = { a: new Date(), b: /test/gi };
const clone = deepClone(obj);
clone.a !== obj.a; // true, different instances

Solution

Reveal solution

function deepClone(value, seen = new Map()) {
  if (value === null || typeof value !== 'object') return value;
  if (seen.has(value)) return seen.get(value);
  if (value instanceof Date) return new Date(value.getTime());
  if (value instanceof RegExp) return new RegExp(value.source, value.flags);
  if (value instanceof Map) {
    const m = new Map();
    seen.set(value, m);
    value.forEach((v, k) => m.set(deepClone(k, seen), deepClone(v, seen)));
    return m;
  }
  if (value instanceof Set) {
    const s = new Set();
    seen.set(value, s);
    value.forEach(v => s.add(deepClone(v, seen)));
    return s;
  }
  const result = Array.isArray(value) ? [] : {};
  seen.set(value, result);
  for (const key of Object.keys(value)) result[key] = deepClone(value[key], seen);
  return result;
}

deep-clone-ii.js

Deep Clone II

hardcodingJavaScriptObjects

Overview

Implement deepClone(value) handling:

Circular references
Date, RegExp, Map, Set
Nested objects and arrays

Constraints

Must not enter infinite loops on circular refs
Preserve prototypes of built-in types

Examples

const obj = { a: new Date(), b: /test/gi };
const clone = deepClone(obj);
clone.a !== obj.a; // true, different instances

Solution

Reveal solution

function deepClone(value, seen = new Map()) {
  if (value === null || typeof value !== 'object') return value;
  if (seen.has(value)) return seen.get(value);
  if (value instanceof Date) return new Date(value.getTime());
  if (value instanceof RegExp) return new RegExp(value.source, value.flags);
  if (value instanceof Map) {
    const m = new Map();
    seen.set(value, m);
    value.forEach((v, k) => m.set(deepClone(k, seen), deepClone(v, seen)));
    return m;
  }
  if (value instanceof Set) {
    const s = new Set();
    seen.set(value, s);
    value.forEach(v => s.add(deepClone(v, seen)));
    return s;
  }
  const result = Array.isArray(value) ? [] : {};
  seen.set(value, result);
  for (const key of Object.keys(value)) result[key] = deepClone(value[key], seen);
  return result;
}

NameTopicDifficulty

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