deep copy of javascript object (version ES6)

deepcopy.js

	//
	// Precondition: 1. "obj is not allowed to contain references pointing to itself"
	// (function calls itself recursively, so this precondition
	// must be matched by all contained objects)
	//
	functiondeepCopy(obj)
	{
	if(typeofobj!=='object'\|\|obj===null)
	returnobj

	constnewObject=(obj.constructor===Array ? [] : {})

	constkeys=Object.keys(obj)
	for(constiinkeys){
	newObject[keys[i]]=deepCopy(obj[keys[i]])
	}

	returnnewObject
	}

	consto1={
	a: null,
	b: 1,
	c: 'string',
	d: [1,2,3,{4: null}],
	e: {
	shared_value: 'deep copy',
	},
	}

	// test shallow vs. deep copy

	consto1_shallow_copy=Object.assign({},o1)
	consto1_deep_copy=deepCopy(o1)

	o1.e.shared_value='shallow copy'

	console.log("o1_shallow_copy: ",o1_shallow_copy)
	console.log("o1_deep_copy: ",o1_deep_copy)

	//
	// Supports objects with self references
	//
	functiondeepCopy(obj)
	{
	constself_refs=newMap()

	functiondeepCopySafe(obj)
	{
	if(typeofobj!=='object'\|\|obj===null)
	returnobj

	if(self_refs.has(obj))
	returnself_refs.get(obj)

	constnewObject=(obj.constructor===Array ? [] : {})
	self_refs.set(obj,newObject)

	constkeys=Object.keys(obj)
	for(constiinkeys){
	newObject[keys[i]]=deepCopySafe(obj[keys[i]])
	}

	returnnewObject
	}

	returndeepCopySafe(obj)
	}

	// test circular linked list

	consto2={
	value: 2,
	next: null,
	}
	consto3={
	value: 3,
	next: o2,
	}
	o2.next=o3

	consto4=deepCopy(o2)

	console.log("linked list:",o2)
	console.log("deep copy of linked list:",o4)