ObjectUtilities including deep merging of multiple objects

object-utilities.ts

export class ObjectUtilities {
    public static merge<T extends object = object>(target: T, ...sources: T[]): T {
        if (!sources.length)
            return target;

        const source = sources.shift();
        if (source === undefined)
            return target;

        if (ObjectUtilities.isMergeableObject(target) && ObjectUtilities.isMergeableObject(source))
            Object.keys(source).forEach((key: string) => {
                if (ObjectUtilities.isMergeableObject(source[key])) {
                    if (!target[key])
                        target[key] = {};

                    ObjectUtilities.merge(target[key], source[key]);
                } else
                    target[key] = source[key];
            });

        return ObjectUtilities.merge(target, ...sources);
    }

    public static isObject<T>(item: T): boolean {
        return item !== null && typeof item === 'object';
    }

    private static isMergeableObject<T>(item: T): boolean {
        return ObjectUtilities.isObject(item) && !Array.isArray(item);
    }
}