Different methods in JavaScript to do deep clone for plain object without libraries

1, use JSON.parse and JSON.stringify, but it has many issues, major one is can’t handle Date type.

var cloned = JSON.parse(JSON.stringify(objectToClone));

2, refer to this, mainly ideas is loop the properties one by one, and go into children, also need to handle ‘Function’, ‘Symbol’, ‘WeakSet’, etc. all possible data types in JavaScript :

https://stackoverflow.com/questions/122102/what-is-the-most-efficient-way-to-deep-clone-an-object-in-javascript

function clone(obj) {
    if (obj === null || typeof (obj) !== 'object' || 'isActiveClone' in obj)
        return obj;

    if (obj instanceof Date)
        var temp = new obj.constructor(); //or new Date(obj);
    else
        var temp = obj.constructor();

    for (var key in obj) {
        if (Object.prototype.hasOwnProperty.call(obj, key)) {
            obj['isActiveClone'] = null;
            temp[key] = clone(obj[key]);
            delete obj['isActiveClone'];
        }
    }
    return temp;
}

also there are more examples could refer to, for example this version needs ES6 supports https://stackoverflow.com/questions/40291987/javascript-deep-clone-object-with-circular-references

function deepClone(obj, hash = new WeakMap()) {
    // Do not try to clone primitives or functions
    if (Object(obj) !== obj || obj instanceof Function) return obj;
    if (hash.has(obj)) return hash.get(obj); // Cyclic reference
    try { // Try to run constructor (without arguments, as we don't know them)
        var result = new obj.constructor();
    } catch(e) { // Constructor failed, create object without running the constructor
        result = Object.create(Object.getPrototypeOf(obj));
    }
    // Optional: support for some standard constructors (extend as desired)
    if (obj instanceof Map)
        Array.from(obj, ([key, val]) => result.set(deepClone(key, hash), 
                                                   deepClone(val, hash)) );
    else if (obj instanceof Set)
        Array.from(obj, (key) => result.add(deepClone(key, hash)) );
    // Register in hash    
    hash.set(obj, result);
    // Clone and assign enumerable own properties recursively
    return Object.assign(result, ...Object.keys(obj).map (
        key => ({ [key]: deepClone(obj[key], hash) }) ));
}

Anyway, I recommend to use JavaScript library ‘clone‘ for the deep clone, it could handle circular reference correctly.

If you need to create more complex feature to re-create (serialization) new instance from source object or JSON string (and use TypeScript), I prefer to use this https://github.com/typestack/class-transformer The ‘class-transformer’ doesn’t force you to describe the class with decorator (of course you could do it, and have to if you need rich features), it is good point I prefer to.

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