45. Deep Clone II - Circular References

Implement deepClone with support for circular references, Map, Set, Date, and RegExp.

1) Supported values

• Primitives, arrays, and plain objects
• Map (clone keys and values)
• Set (clone values)
• Date
• RegExp

2) Circular references

• Prevent infinite recursion.
• Preserve graph shape (self-reference in source should map to self-reference in clone).
• Use a visited structure (typically WeakMap).

3) Independence

• Mutating cloned nested values must not mutate originals.

4) Scope note

• Function cloning and symbol-key-specific behavior are out of scope for this level.

Examples

const obj = { name: "A" }
obj.self = obj
const cloned = deepClone(obj)

cloned !== obj              // true
cloned.self === cloned      // true

const map = new Map([["k", { n: 1 }]])
const cloned = deepClone(map)
cloned.get("k").n = 2

map.get("k").n // 1