use-s-react/dist/functions/deep-assign.js

useS is a minimal yet powerful React hook for managing both local and global state — with zero boilerplate

export function deepAssign(target, source) {
    for (const key in source) {
        const sourceValue = source[key];
        const targetValue = target[key];
        if (typeof sourceValue === "object" &&
            sourceValue !== null &&
            !Array.isArray(sourceValue) &&
            typeof targetValue === "object" &&
            targetValue !== null &&
            !Array.isArray(targetValue)) {
            deepAssign(targetValue, sourceValue);
        }
        else {
            target[key] = sourceValue;
        }
    }
    return target;
}