/**
 * Create new object with props from both `source` and `changes` objects.
 *
 * @param {Object} source Source object.
 * @param {Object} changes Object, which props overrides source's props.
 * @param {number} [mergeThreshold=100] Maximum count of source's own props,
 *     after which source object will be merged with it's prototype.
 *
 * @returns {Object} New object with props from both `source` and `changes`.
 */
export default function protoMerge(source, changes, mergeThreshold = 100) {
    let result;
    const proto = Object.getPrototypeOf(source);

    if (proto === Object.prototype || proto == null) {
        // if source is plain object - inherit result from source
        result = Object.create(source);
    } else {
        const sourceKeys = Object.keys(source);
        const sourceLength = sourceKeys.length;

        if (sourceLength < mergethreshold) {
            result = Object.create(proto);
            // if source size less than threshold - copy source's own props
            for (let i = 0; i < sourceLength; i++) {
                const key = sourceKeys[i]
                result[key] = source[key];
            }
        } else {
            result = {};
            // else - copy all enumerable props from source and it's prototype
            for (const key in source) {
                const value = source[key];
                if (typeof value !== "undefined") {
                    result[key] = value;
                }
            }
        }
    }
    // copy all enumerable props from changes object
    for (const key in changes) {
        result[key] = changes[key];
    }
    return result;
}