Deep copy js object

deep-copy.js

export function deepcopy(value) {
    return __deepcopy(value, new WeakMap());
}

export default deepcopy;

const TypedArray = Reflect.getPrototypeOf(Int8Array);

function identity(value) {
    return value;
}

function copyprops(source, target, cache) {
    for (const property in source) {
        target[property] = __deepcopy(source[property], cache);
    }

    return target;
}

// TODO: Copy only outside keys in wrapped constructors

function __deepcopy(value, cache) {
    if (
        (typeof value != "object" || value === null) &&
        typeof value != "function"
    ) {
        return value;
    }

    if (cache.has(value)) {
        return cache.get(value);
    }

    let result;
    let cached = false;

    if (typeof value == "function") {
    } else if (value instanceof RegExp) {
        result = new RegExp(value);
    } else if (value instanceof Map) {
        result = new Map();
        cache.set(value, result);
        cached = true;
        for (const [key, val] of value) {
            result.set(__deepcopy(key, cache), __deepcopy(val, cache));
        }
    } else if (value instanceof Set) {
        result = new Set();
        cache.set(value, result);
        cached = true;
        for (const val of value) {
            result.add(__deepcopy(val, cache));
        }
    } else if (Buffer.isBuffer(value)) {
        result = Buffer.from(value);
    } else if (value instanceof Promise) {
        result = value.then(identity);
    } else if (value instanceof WeakMap || value instanceof WeakSet) {
        // TODO: Improve
        result = value;
    } else if (value instanceof WeakRef) {
        // TODO: Decide what to do with empty refs
        const target = value.deref();

        if (target) {
            const copy = __deepcopy(target, cache);

            // Should deal with recursive structures
            if (cache.has(value)) {
                result = cache.get(value);
            } else {
                result = new WeakRef(copy);
                cache.set(value, result);
            }
        } else {
            result = new WeakRef(Object.create(null));
            cache.set(value, result);
        }

        cached = true;
    } else if (value instanceof Date) {
        result = new Date(value.getTime());
    } else if (value instanceof Error) {
        result = new Error();
    } else if (value instanceof DataView) {
        result = new DataView(value.buffer.slice(0));
    } else if (value instanceof ArrayBuffer || value instanceof TypedArray) {
        result = value.slice(0);
    } else if (value instanceof URL) {
        result = new URL(value);
    } else {
        result = {};
    }

    if (!cached) {
        cache.set(value, result);
    }

    copyprops(value, result, cache);

    return result;
}